788 research outputs found
On the Geometry of the Liapunov-Schmidt Procedure
No full textThe lectures presented by the author are not reproduced here since that material is available in J. Marsden, Qualitative Methods in Bifurcation Theory, Bull. Am. Math. Soc. 84 (1978), 1125–1148, R. Abraham and J. Marsden, Foundations of Mechanics, Second Edition, Addison Wesley (1978), and in J. Marsden and M. McCracken, The Hopf Bifurcation and its Application
Estimating bird abundance : making methods work
No full textIn many bird monitoring Surveys, no attempt is made to estimate bird densities or abundance. instead, counts of one form or another are made, and these are assumed to correlate with bird density. Unless complete Counts Oil Sample plots are feasible, this approach can easily lead to false conclusions, because detectability of birds varies by species, habitat, observer and many other factors. Trends in time of counts often reflect trends in detectability, rather than trends in abundance. Conclusions are further compromised when surveys are conducted at unrepresentative sites. We consider how to avoid these problems. We give a brief description of distance sampling methods, which allow detectability to be estimated. We consider strategies to ease their implementation, to enhance their reliability, to adapt the methods for difficult species, and to deal with circumstances in which representative sampling is problematic. We also consider some of the common problems encountered, and suggest solutions.Peer reviewe
Vipera walser Ghielmi, Menegon, Marsden, Laddaga & Ursenbacher, sp. nov.
No full textVipera walser Ghielmi, Menegon, Marsden, Laddaga & Ursenbacher sp. nov. (Figs 1–4). Holotype Adult female: MSNG 34485, collected in S. Giovanni d’Andorno, on the road to Oropa in the Biella prealps, at about 1300 m a.s.l. by A. Rosazza in the summer of 1930 (Fig. 5). Paratypes One adult male: MSNG 33638 M collected at Monte Rosso del Croso, on 30 August 1933. One juvenile male: MSNG 33637 B and one subadult male: MSNG 30818 C collected at Alpe Finestre by Felice Capra, respectively, on 28 July 1930 and 15 August 1928. One adult female: MSNG 30818 A, one subadult female: MSNG 30818 B, and two juvenile females: MSNG 33637 C and MSNG 33637 D collected by Felice Capra at Alpe Finestre between August 1928 and August 1939. One juvenile female: MSNG 30286 collected by F. Capra at Monte Rosso del Croso on 12 September 1934; one adult female MSNG 33637 A collected by F. Capra at Alpe le Piane on 5 August 1937; one adult female MSNG 41663 collected by A. Margiocco at Piedicavallo in September 1967. Type locality San Giovanni d’Andorno, strada per Oropa at 1300 m a.s.l. in the Alps north of town of Biella, a subrange of the Pennine Alps, north-western Italy. Differential diagnosis Vipera walser sp. nov. is generally similar to the species of the subgenus Pelias and can be confused with V. berus, which co-occurs on the Alps in allopatry (Fig. 6, Table 2). The species differs in a generalized higher count of cephalic scales, in particular the ones listed below (V. berus in parentheses): higher number of crown scales: 7–30, mean 17.4 (versus 4–22, mean 13.0); loreals: 4–15, mean 9.36 (versus 2–12, mean 6.72); and, to a lesser extent, perioculars: 16–23, mean 19.8 (versus 13–23, mean 18.4) (see Table 2). V. walser, in contrast to V. berus, also shows a marked tendency towards fragmentation of the cephalic large shields: the parietal scales are often completely broken down into several smaller scales: 2–14, mean 6.3 (versus 2–10, mean 2.4; see also Fig. 7). Less commonly, also the frontal scale is fragmented into smaller scales. Some individuals exhibit a dorsum of the head covered in small, irregular scales, like in V. aspis. V. walser has between 1.5 and 2 rows of subocular scales on both sides of the head in 85 % of the analysed specimens (V. berus has typically one row of suboculars, with the exception of some populations in the southern Alps). The dorsal zigzag is often broken down into separate bars as in Vipera aspis (Linnaeus, 1758) or Vipera berus bosniensis (see Fig. 6). Despite the lack of a strictly diagnostic morphological character, V. walser can be readily distinguished from populations of V. berus from Central and northern Europe by a combination of several characters (e.g. the number of subocular scales, fragmentation of parietals and number of apicals). Identification based solely on observation of external morphology is less obvious if individuals of V. berus from southern Alps are considered. Despite this, discriminant analysis correctly identified individuals to species in 94 % of females and 88 % of males, based on a set of analysed characters (see Figs 2 and 3). The mean p-distance, based on a combined dataset of about 3000 base pairs of mitochondrial genes, between V. berus and. walser is 5.36 %. Based on our current knowledge of its distribution, Vipera walser is restricted to the Alps north of town of Biella, a subrange of the Pennine Alps, west of the river Ticino, north-western Italy (Fig. 8). The differences in cephalic scale count between Vipera walser and. berus are shown in Table 2: Crown scales (females: t 45,49 = 4.81, p <0.0001; males: t 28,71 = 5.20, p <0.0001); loreals (females: t 94,59 = - 7.52, p <0.0001; males: t 62,67 = - 4.43, p <0.0001); and, in females only, perioculars (female: t 64,16 = 5.33, p <0.0001; males: t 17,25 = - 0.16, p = 0.87) and apicals (females: t 32,86 = 2.14, p = 0.04; males: t 18,0 8 = - 0.12, p = 0.91); the number of scales between the eyes and the supralabials are higher (females: t 66,40 = 5.85, p <0.0001; males: t 37,93 = 7.90, p <0.0001). Paratype variations Details and meristics for the analysed individuals, including the type series, are summarized in Table 3. Description of the holotype Adult female conserved in 70 % EtOH in rather good condition, with the body slightly swollen probably due to preservation. Snout-vent length (SVL) 515.2 mm, tail 55.0 mm, ratio of tail proportion (/ SVL) 0.107. Two apical scales in contact with the rostral. Head oval shaped, wider in the temporal region, neck not very distinct, snout rounded. Frontal single, and larger than any other scale on head, five parietals. Rostral slightly higher than broader; nasal roundish, nostril circular and approximately in the centre of the nasal; one internasal on left side of the head and two on right side; perioculars 11 – 10; two rows of suboculars on both sides of the head; circumoculars separated from nasals by six and five loreal scales, respectively, on right and left side; supralabials 9 – 9, the fourth and the fifth below the eye; 147 ventrals; 31 divided subcaudals (excluding spine); anal entire; 21 scale rows at midbody. Dorsum is brown in colour with a continuous and regular darker brown zigzag. Head is reddish-brown with scattered, faint darker markings, and a more obvious inverted V-shaped ornamentation just before the neck. Labials are paler with black markings bordering the edges. A wide black band is present on both sides of the head between the postoculars and the neck. Ventrals are black, with white, scattered speckling along the lower margin of the scales and, more consistently, on both scale extremes by the first row of dorsals. Etymology Vipera walser sp. nov. is named after, and dedicated to, the Walser people with whom it shares an extraordinary beautiful and wild area of the south-western Alps. Discussion Delineating species boundaries correctly is crucial for the discovery of life’s diversity because it determines whether or not different individual organisms are members of the same entity (Dayrat 2005). Most evolutionary biologists now agree that species are separately evolving lineages of populations or meta-populations, with disagreements remaining only about where along the divergence continuum separate lineages should be recognized as distinct species (Padial et al. 2010). The Mitochondrial Tree Morphological Character Congruence (MTMC) approach has been formalized by Miralles and Vences (2013) and represents the most common practice in zootaxonomic studies, combining evidence from DNA sequences and morphological data. Integrative taxonomy has been also proposed as a framework to bring together conceptual and methodological developments aimed to describe, classify and name new taxa (Padial et al. 2010). The integration by congruence approach of integrative taxonomy follows the principle that different lines of evidence should be combined to delimit species, such as genetic (mtDNA and nuclear), morphological, distributional and ecological data. The genetic differentiation between. walser and. berus, both on mitochondrial and nuclear DNA, is beyond known values between well-established species within the same subgenus. The status of full species is further confirmed by the bPTP analysis and as a morphological line of evidence by the discriminant analysis. Furthermore, there is no evidence of introgression from, for example,. berus as confirmed by the numerous individuals analysed for mtDNA, and the strong difference between these two species on the two nuclear genes sequenced. The species, within the alpine context, inhabits an ecologically peculiar area, characterized by some the highest rainfall of the whole alpine region (Mercalli et al. 2008). The discovery of the. walser lineage was particularly unexpected, especially in this biologically well-known and densely sampled region of western Europe. The species shows closer genetic affinities with, on one hand,. darevskii and. kaznakovi, species occurring in the Caucasus and, on the other, with the. ursinii complex (see Table 1), than with the. berus complex. Limited phylogenetic support suggests a simultaneous split between. ursinii complex,. kaznakovi (Georgia) complex and. walser (possible trichotomy). Moreover, the ML phylogenetic reconstruction regrouped. walser with the. kaznakovi (Georgia) complex, whereas the genetic distance displayed more affinities with the. ursinii complex. Until now, it was believed that western Europe was colonized from the Pelias subgenus only by. berus (including. seoanei Lataste, 1879, restricted to the Iberian peninsula), and the. ursinii group, which occupy distinct habitats (cold forest for. berus and steppe areas for. ursinii; Saint Girons 1978). The presence of a new distinct lineage, more related to the Caucasian vipers, strongly suggests an additional, more recent, colonization of western Europe (from the. kazankovi complex or during the split between the. kaznakovi complex and. ursinii complex) than the one involving the. berus group, and possibly one that was concurrent with that of. ursinii (Early Pliocene; Ferchaud et al. 2012). Given that the European viper species tend to exclude each other geographically, resulting in limited portions of overlapped ranges (Saint Girons 1978), we can assume that. walser found refugial areas different from those of. berus during the numerous glaciations of the Pleistocene. Currently, both. berus and. walser seem to occupy very similar habitats, suggesting a possible competition (or ecological differentiation as that between. aspis and. berus; Guillon et al. 2014). It is, however, possible that, like V. kaznakovi,. walser can tolerate warmer temperatures than can. berus so long as sufficient humidity is present. Yet, this possibility needs to be investigated as it could have important implications for future conservation programmes. Near-future threats and conservation Vipera walser appears to occur only in a very limited area in the Alps north of Biella (Fig. 8). It is very likely that all native populations of adder south of the Alps and west of the river Ticino belong to the species herein described. Based on the Italian Atlas of Amphibians and Reptiles (Sindaco et al. 2006), the current distribution area (‘extent of occurrence’) is almost certainly <1000 km 2. Consequently,. walser should be classified as ‘endangered’ according to (2014) Red List criteria B 1 a/B 2 a. If we consider that the population is strongly fragmented, or that the actual area of occupancy is probably <500 km 2 and fragmented (Red List Categories and Criteria: Version 3.1. Second edition), then. walser appears to be among the most threatened vipers in the world. The new taxon’s sister species. darevskii, with area of occupancy <10 km 2, is now listed as ‘critically endangered’ (Tuniyev et al. 2009), whereas. kaznakovi (related to. darevskii and thus to. walser) is considered ‘endangered’, meaning that the entire clade is highly threatened with extinction. Within its restricted range,. walser appears to be quite common in suitable habitat. However, to date, no systematic survey has been undertaken, either to estimate its population density or identify its habitat requirements. Such surveys are clearly a priority for the future research. Estimates of current abundance, using mark–recapture or distance sampling (e.g. Mazerolle et al. 2007), would be useful to determine total population size and trends, and to more precisely assign the species to a Red List category. Occupancy modelling (Larson 2014) might also be suitable to determine areas of occupancy at appropriate scales. Perhaps more important would be detailed studies of the species’ precise habitat requirements, to determine how past and current land use changes have affected the species, and how they might be altered to benefit the species in the near future. Based on our preliminary observations, this species inhabits open areas, often with rocky outcrops (Fig. 9), and may not tolerate woodland unless it is very sparse. European mountains experienced a long period of agricultural/agropastoral expansion from the Late Middle Ages to the 19 th century, with large areas of the Alps converted to upland grasslands and heathlands (e.g. Vives et al. 2014). These open landscapes were presumably beneficial for. walser. However, the decline in agropastoral activities in the last 100 years and associated afforestation (Carlson et al. 2014; Garbarino et al. 2014) is probably the greatest threat to the species, and it is an urgent priority to assess such changes within the range of. walser. More immediate and major threats in the short term are culling and collection. Indeed, the description of several new vipers species (e.g.. kaznakovi and Montivipera wagneri (Nilson & Andŕen, 1984)), as well as the attraction of being peculiar and rare (e.g. Macrovipera schweizeri (Werner, 1935), has led to the illegal collection of numerous individuals for the international pet trade (Nilson et al. 1999, http://www.iucnredlist.org), causing local extinctions. Because this species occurs only in Italy, we strongly suggest that a specific legal protection for the species should be implemented very quickly. Longer term prospects and climatic change Of course, it can be argued that. walser, as a restricted-range relic species, is likely heading down an evolutionary dead-end path (Allendorf and Luikart 2007), in the sense of Darwin’s ‘wreck of ancient life’ (Darwin 1859) or Jeannel’s ‘fossiles vivants’ (Jeannel 1943). Its eventual natural extinction may take many millennia, but its ability to survive the next 100 years may hang on two important aspects of its biology. First, there is a real lack of genetic variability within the population as compared to that in other vipers (e.g. Ursenbacher et al. 2006 a, b; Ferchaud et al. 2011). The population is already fragmented into two main subpopulations, and, presumably, the complex topography of ridges and valleys may work to further isolate populations, as in. berus (Ursenbacher et al. 2009). A high priority for future study is an examination of habitat suitability at the landscape scale coupled with research on dispersal mechanisms and ability in the species. Second, and related to the above, its ability to withstand or adapt to climatic change expected to take place within its range will be crucial. The current habitat of. walser is restricted to an area of around 800 km 2 within a few valleys, which experience some of the highest rainfall in the Alps (Mercalli et al. 2008). Point estimates of annual rainfall from presence locations within its area of occupancy range from 1018 to 1604 mm (mean = 1348 mm ± 111) and mean minimum temperature between May and October from 3.1 to 10.0° C (mean = 6.1 ± 1.2 ° C SD). Climate models (CMIP 5 IPPC Fifth Assessment; www.worldclim.org) indicate that in the next 20 years, these valleys will become far wetter (mean = 1536 mm ± 129 SD) and warmer (mean = 8.5 ± 1.2 ° C SD; Fig. 10). Consequently, species distribution modelling, and how this distribution might change under realistic climate change scenarios, especially including the influence of habitat and habitat change and dispersal ability (e.g. Pearson and Dawson 2003), is clearly a priority. Conclusion The present study described and named a new viper species,. walser, which shows strong genetic divergence and clear morphological differentiation from all other known European viper species. The new taxon occurs in a restricted area of the southwestern Italian Alps and shows close affinities with the Caucasian species. dinniki,. darevskii and. kaznakovi, opening unexpected and interesting biogeographic scenarios. The very small extent of occurrence of the new species implies a particularly high threat level, and thus conservation managements should be developed. The protection of its habitat, the limitation of the forest regrowth, but also the evaluation of its likely future distribution given climatic changes (for the long term) or struggle against culling (short term) are key elements to investigate. Involvement of local authorities, foundations and other stakeholders will be crucial in realizing effective protection of this species.Published as part of Samuele Ghielmi, Michele Menegon, Stuart J. Marsden, Lorenzo Laddaga & Sylvain Ursenbacher, 2016, A new vertebrate for Europe: the discovery of a range-restricted relict viper in the western Italian Alps, pp. 161-173 in J. Zool. Syst. Evol. Research 54 (3) on pages 164-171, DOI: 10.1111/jzs.12138, http://zenodo.org/record/19190
Software Support for Podcasting Mobile Lecture Content for Education in Sub-Sahara African Universities
No full textPodcasting is fast gaining traction in developing regions as a means to augment classroom instruction. Commercial podcasting tools such as Apple’s Leopard Server, Tele-task and OpenEya, despite being successfully used in the developed world (where Internet connections are fast and students have powerful multimedia devices) may not be directly transferable to the developing world due to social, economic, technical, political and cultural differences. Thus, we need to gain an understanding of podcasting in developing world Higher Education Institutions in order to develop appropriate tools. Moreover, past podcasting research shows that there is an acute lack of theoretical models, conceptual frameworks as well as evaluation models.
Consequently, this thesis employs User Centered Design techniques to offer guidance for contextual podcasting design. In particular, Participatory Action Research was used to gain a deep knowledge of developing world academics’ work context and needs, identify specific requirements, develop a novel podcasting application (called MLCAT – Mobile Learning Content Authoring Tool) and ensure that they accept and use the technology. The final stage of this research was an eight week prototype evaluation aimed at evaluating MLCAT. The main contributions of this thesis are: the identification of design opportunities for podcasting tools (using Participatory Action Research) to support faculty in developing HEIs; a podcasting information ecology model; an adaptation of podcasting to developing country HEIs and a series of design and methodological contributions relating to the design of podcasting tools and other information systems.
Findings suggest that academics and students alike valued the need for a seamless podcast production process – one that does not require expensive and sophisticated infrastructure; the ability to author short podcasts or package them into small chunks; the use of Bluetooth for access and sharing podcasts as well as building on tools already in their possession as opposed to completely new ones. This research is one of the few works that relate to podcasting in developing world Higher Education Institutions. It has implications for the design of podcasting applications through an appreciation of the usefulness of research and practice in Human-Computer Interaction for development and how easily this can be adapted to understand and improve mobile learning development practice
Apaf-1 and caspase-9 accelerate apoptosis, but do not determine whether factor-deprived or drug-treated cells die
No full textApoptosis after growth factor withdrawal or drug treatment is associated with mitochondrial cytochrome c release and activation of Apaf-1 and caspase-9. To determine whether loss of Apaf-1, caspase-2, and caspase-9 prevented death of factor-starved cells, allowing them to proliferate when growth factor was returned, we generated IL-3–dependent myeloid lines from gene-deleted mice. Long after growth factor removal, cells lacking Apaf-1, caspase-9 or both caspase-9 and caspase-2 appeared healthy, retained intact plasma membranes, and did not expose phosphatidylserine. However, release of cytochrome c still occurred, and they failed to form clones when IL-3 was restored. Cells lacking caspase-2 alone had no survival advantage. Therefore, Apaf-1, caspase-2, and caspase-9 are not required for programmed cell death of factor-dependent cells, but merely affect its rate. In contrast, transfection with Bcl-2 provided long-term, clonogenic protection, and could act independently of the apoptosome. Unlike expression of Bcl-2, loss of Apaf-1, caspase-2, or caspase-9 would therefore be unlikely to enhance the survival of cancer cells.Paul G. Ekert, Stuart H. Read, John Silke, Vanessa S. Marsden, Hitto Kaufmann, Christine J. Hawkins, Robert Gerl, Sharad Kumar, and David L. Vau
Discontinuous molecular dynamics for semiflexible and rigid bodies
No full textA general framework for performing event-driven simulations of systems with semiflexible or rigid bodies interacting under impulsive forces is outlined. The method consists of specifying a means of computing the free evolution of constrained motion, evaluating the times at which interactions occur, and determining the consequences of interactions on subsequent motion. Algorithms for computing the times of interaction events and carrying out efficient event-driven simulations are discussed. The semiflexible case and the rigid case differ qualitatively in that the free motion of a rigid body can be computed analytically and need not be integrated numerically. (c) 2007 American Institute of Physics.PT: J; CR: ABRAMOWITZ M, 1965, HDB MATH FUNCTIONS F ALDER BJ, 1959, J CHEM PHYS, V31, P459 ALDER BJ, 1960, J CHEM PHYS, V33, P1439 ALLEN MP, 1987, COMPUTER SIMULATION ALLEN MP, 1989, COMPUT PHYS REP, V9, P301 ANDERSEN HC, 1983, J COMPUT PHYS, V52, P24 BARAFF D, 1989, COMPUT GRAPH, V23, P223 BARAFF D, 1992, THESIS CORNELL U BRENT RP, 1973, ALGORITHMS MINIMIZAT CARTER EA, 1989, CHEM PHYS LETT, V156, P472 CHAPELA GA, 1984, MOL PHYS, V53, P139 CHAPELA GA, 1989, CHEM PHYS, V129, P201 CICCOTTI G, 2004, J STAT PHYS, V115, P701 DELAPENA LH, UNPUB DELAPENA LH, 2005, J CHEM PHYS, V126 DEMICHELE C, 2006, J PHYS CHEM B, V110, P8064 DONEV A, 2005, J COMPUT PHYS, V202, P737 DONEV A, 2005, J COMPUT PHYS, V202, P765 ERPENBECK JJ, 1977, STAT MECH B FIXMAN M, 1974, P NATL ACAD SCI USA, V71, P3050 FRENKEL D, 2004, UNDERSTANDING MOL DY GALASSI M, 2005, GNU SCI LIB REFERENC GOLDSTEIN H, CLASSICAL MECH JACOBI CGJ, 1849, J CRELLE, V39, P293 KNOPP K, 1947, THEORY FUNCTIONS 2 LANDAU LD, 1976, MECHANICS LUBACHEVSKY BD, 1991, J COMPUT PHYS, V94, P255 MARIN M, 1993, J COMPUT PHYS, V109, P306 MARIN M, 1995, COMPUT PHYS COMMUN, V92, P214 MARSDEN JE, 2002, INTRO MECH SYMMETRY MASUTANI Y, 1994, P IEEE INT C ROB AUT, V2, P1066 MELCHIONNA S, 2000, PHYS REV E A, V61, P6165 MOSHIER SL, 1989, METHODS PROGRAMS MAT PRESS WH, 1992, NUMERICLA RECIPES FO RAMSHAW JD, 1986, PHYS LETT A, V116, P110 RAPAPORT DC, 1980, J COMPUT PHYS, V34, P184 RAPAPORT DC, 2004, ART MOL DYNAMICS SIM RUEB AS, 1834, THESIS UTRECHT NETHE RYCKAERT JP, 1977, J COMPUT PHYS, V23, P327 TUCKERMAN ME, 1999, EUROPHYS LETT, V45, P149 TUCKERMAN ME, 2001, J CHEM PHYS, V115, P1678 VANZON R, IN PRESS J COMPUT PH VANZON R, 2002, PHYS REV E 1, V65 WHITTAKER ET, 1937, TREATISE ANAL DYMANI; NR: 44; TC: 1; J9: J CHEM PHYS; PG: 13; GA: 138VLSource type: Electronic(1
The relationship between population density, habitat position and habitat breadth within a neotropical forest bird community
No full textWe examined the relationship between local abundance, habitat position and habitat breadth across bird species in a large Atlantic forest reserve in Brazil. This appears to be the first such study for any rainforest taxon. Habitat position for a species was its mean foraging height, along with the mean scores on three principal habitat axes for census stations at which it was recorded. Habitat breadth was the standard deviation of recorded foraging heights and the standard deviations of "positive" station scores on the habitat axes. We also examined differences in habitat position and breadth between endemic and wide-ranging taxa and amongst dietary groups. Amongst 31 species for which density estimation was possible, there were no correlations between local abundance and breadth of habitat use on any of the habitat axes. Breadth of habitat used did not vary with degree of endemism, but herbivores used a greater breadth of habitats on the axis describing canopy closure than did omnivores. Habitat position did not vary with endemic status, but herbivores preferred higher-biomass habitats than faunivores, and higher foraging heights than either faunivores or omnivores. Local abundance was linked weakly to habitat position with commoner species tending to forage in the lower strata of open-canopied areas. The 31 most commonly recorded species tended to occupy "middle-range" habitat positions, while 28 rarer species occupied habitats toward one or other end of the vegetation axes. These results suggest an association between the local abundance of a species and its habitat position, and especially its preference for common or mid-range habitats, rather than with its ability to utilise a wide range of habitats
The response of a New Guinean avifauna to conversion of forest to small-scale agriculture
No full textIn comparison with other tropical forest land uses such as selective logging, little is known of the impacts on wildlife of the many forms of small-scale agriculture practised across the tropics. We present density estimates, derived using a point count distance sampling method, for 31 bird species in primary forest, old abandoned gardens and active/recently abandoned gardens at two altitudes in the Crater Mountain Wildlife Management Area (CMWMA), Papua New Guinea. There were clear habitat differences between the six habitat/altitude categories, with, for example, clines in tree sizes and canopy cover from highest values in primary forest to lowest values in current gardens. At lower altitudes, primary forest held highest densities of most species, whereas at higher altitudes, old abandoned gardens had greater densities of many birds, especially insectivores. CANOCO was used to ordinate bird species with respect to major habitat gradient axes. Major axes were associated with differences in bird responses to forest conversion as well as altitudinal differences in species composition. Most important was that several insectivores (especially monarchs, fantails, etc.) formed a cluster of species associated with intact, high-biomass forest. We suggest that most species reacted moderately to habitat changes currently occurring, and this may be due in part to the fact that only a small proportion of the landscape at CMWMA has been converted to agriculture (around 13% may be current or recently abandoned gardens). There were, however, species with comparatively low densities in agricultural habitats and these included several insectivores, the terrestrial Blue Jewel-babbler Ptilorrhoa caerulescens, and three out of four birds of paradise.
Shifting cultivation (including slash-and-burn and gardening) is a major land use and cause of deforestation in tropical regions (Fujisaka et al. 1996, Raman 2001). In fact, Myers (1991) described the landless peasants ('shifted cultivators') practising shifting cultivation as the main agent of tropical forest loss, accounting for at least 60% of deforestation. Despite the large area of the tropics over which it is practised, the great diversity of agricultural systems, and the debate as to the degree to which such land uses contribute to biodiversity loss (Myers 1991, Halladay & Gilmour 1995), few papers have assessed the impact on wildlife of the myriad small-scale agricultural systems practised (for birds see the partial review by Dunn 2004; see also Blankespoor 1991, Thiollay 1995, Raman 2001, Naidoo 2004).
Here, we present one of the first multi-species bird studies examining differences in bird abundance between primary forest and small-scale 'garden' agriculture plots. We present population density estimates for 31 forest bird species in primary forest, current and recently abandoned gardens, and old gardens within two altitude bands (432–650 m and 651–935 m) at Crater Mountain Wildlife Management Area (CMWMA), a hillforest region of eastern New Guinea. The last two habitat categories represent small-scale mixed agriculture/agroforestry, the main generic form of forest alteration across much of Papua New Guinea (Levett & Bala 1994). In CMWMA, agricultural plots are small and exist within an extensive matrix of little-disturbed forest and this mosaic of low-intensity and diverse gardens is rather different from the agricultural landscapes of other studies (Thiollay 1995, Estrada et al. 1997). It is also, however, the type of traditional low-intensity agricultural system that is under threat as a result of agricultural expansion and homogenization in many areas of the tropics (Allen 1985, Thiollay 1995).
Furthermore, the density estimates we present are, in almost every species, the first indications of absolute abundance for birds on New Guinea, so we compare bird densities and reactions to habitat change with those recorded on nearby islands and draw some conclusions as to the likely impact of habitat change on the avifauna as a whole
Preventative therapies for healthy women at high risk of breast cancer
No full textIvana Sestak Centre for Cancer Prevention, Wolfson Institute of Preventive Medicine, Queen Mary University of London, Charterhouse Square, London, UKAbstract: Tamoxifen has been shown to reduce the risk of developing estrogen receptor (ER)-positive breast cancer by at least 50%, in both pre- and postmenopausal women. The current challenge is to find new agents with fewer side effects and to find agents that are specifically suitable for premenopausal women with ER-negative breast cancer. Other selective estrogen receptor modulators (SERMs), such as raloxifene, arzoxifene, and lasofoxifene, have been shown to reduce the incidence of breast cancer by 50%–80%. SERMs are interesting agents for the prevention of breast cancer, but longer follow-up is needed for some of them for a complete risk–benefit profile of these drugs. Aromatase inhibitors have emerged as new drugs in the prevention setting for postmenopausal women. In the Mammary Prevention 3 (MAP3) trial, a 65% reduction in invasive breast cancer with exemestane was observed, and the Breast Cancer Intervention Study-II trial, which compared anastrozole with placebo, reported a 60% reduction in those cancers. Although SERMs and aromatase inhibitors have been proven to be excellent agents in the preventive setting specifically for postmenopausal women and ER-positive breast cancer, newer agents have to be found specifically for ER-negative breast cancers, which mostly occur in premenopausal women. Keywords: breast cancer, preventive therapy, selective estrogen receptor modulators, aromatase inhibitors, high-risk wome
Overlap effects on electron transmission through doped molecular wires
No full textThe electron transmission properties of a molecular wire, containing a single impurity, are investigated in the context of the tight-binding approximation. The inclusion of overlap gives rise to nonorthogonal orbitals, whose treatment requires a tensorial formalism to obtain the Green function arising in the Lippmann-Schwinger equation approach to the transmission probability T(E). The presence of overlap has profound effects on the T(E) curves. In particular, two antiresonances appear, which are governed by different conditions. The T(E) behavior, throughout the parametric space in question, is described in detail. It is clear that a viable theory of electron transmission should take account of overlap. The tensorial procedure, adopted here, provides a direct means of doing so.PT: J; CR: ARTACHO E, 1991, PHYS REV A, V43, P5770 AVIRAM A, 1998, MOL ELECT SCI TECHNO DAVISON SG, 1992, BASIC THEORY SURFACE EMBERLY E, 1998, PHYS REV LETT, V81, P5205 EMBERLY EG, 1999, J PHYS-CONDENS MAT, V11, P6911 ENGLISH RA, 1994, PHYS REV B, V49, P8718 ENGLISH RA, 1998, J PHYS-CONDENS MAT, V10, P4423 FARCHIONI R, 2001, ORGANIC ELECT MAT JORTNER J, 1997, MOL ELECT LIPPMANN BA, 1950, PHYS REV, V79, P469 LOHEZ D, 1983, PHYS REV B, V27, P5007 MARSDEN JE, 1973, BASIC COMPLEX ANAL MIRABELLA DA, 1994, AM J PHYS, V62, P162 RATNER MA, 1990, J PHYS CHEM-US, V94, P4877 SAUTET P, 1988, PHYS REV B, V38, P12238 SLATER JC, 1930, PHYS REV, V35, P509; NR: 16; TC: 5; J9: PHYS REV B; PG: 7; GA: 687MFSource type: Electronic(1
- …
