1,975 research outputs found
Searches For New Bosons Coupling To e-q Pairs At HERA And Other Colliders
The early observation at HERA of an excess of events compared to the
expectation from the Standard Model in very short distance
deep-inelastic scattering processes has renewed the interest in the search for
new physics which could manifest in electroweak-like interactions. New
preliminary results from the H1 and ZEUS experiments making use of all
available data are reviewed here, with an emphasis on the search for new
bosons possessing Yukawa couplings to lepton-quark pairs. The sensitivity of
HERA to leptoquarks, and to squarks of R-parity violating supersymmetry, is
confronted to existing indirect constraints from rare and forbidden
semi-leptonic decays, atomic parity violation and neutrinoless double-beta
decay, as well as to direct constraints from LEP and Tevatron colliders. The
HERA and Tevatron colliders are found to offer exciting prospects for new
physics, accessing yet unexplored domains of the mass-coupling plane. Possible
striking manifestation of explicit lepton flavour violation is also discussed.Comment: 27 pages, 16 figures. Proceedings of the WEIN'98 Symposium (June
1998
Search for Particles and Forces Beyond the Standard Model at HERA ep and Tevatron p\bar{p} Colliders
A review of searches for physics beyond the Standard Model carried out at
high energy lepton-hadron and hadron-hadron facilities is presented, with
emphasis on topics of interest for future data taking at the upgraded Tevatron
and HERA colliders. The status and discovery prospects are
discussed for leptoquarks, Technicolour and supersymmetry, forbidden lepton and
quark flavour-changing processes, extra gauge bosons, excited states of
composite fermions, generic contact interactions and extra compactified
dimensions.Comment: 64 pages, 34 figures, submitted for publication in "Progress in
Particle and Nuclear Physics
Observability of the Heavy Neutral SUSY Higgs Bosons Decaying into Neutralinos
A prospective study for the observation of the decays of heavy neutral Higgs bosons into supersymmetric particles at the Large Hadron Collider is presented . The analysis focuses on the decay of the Higgs bosons into a pair of next-to-lightest neutralinos chi2, followed by the cascade down to the lightest neutralino, chi2 to l+ l- chi1. The final state is characterized by the presence of four isolated and missing tranverse energy. The parameter space of the minimal Supergravity model is explored and favorable regions for the observation of the A/H bosons are identified. The A/H bosons could be discovered in the 2e2mu channel in the mass region mA,H (250,400) GeV/c2 with an integrated luminosity of 30 fb-1
Observability of the heavy neutral SUSY Higgs bosons decaying into neutralinos at the LHC
Research Note From Collaboration; A prospective study for the observability of heavy neutral Higgs bosons decaying into supersymmetric particles at the Large Hadron Collider with the CMS detector is presented. The analysis focuses on the decay of the Higgs bosons into a pair of next-to-lightest neutralinos Ï02, followed by the cascade down to the lightest neutralino, Ï02 â l+l-Ï01. The final state is characterized by the presence of four isolated leptons and missing transverse energy. The parameter space of the minimal supergravity model is explored and favourable regions for the observation of the A0/H0 bosons are identified. The A0/H0 bosons could be discovered in the 2e2ÎŒ channel in the mass region 250 lesssim mA/H lesssim 400 GeV/c2 with an integrated luminosity of 30 fb-1
Barotraumatisme chez les poissons dâeau douce et impact de la perforation de la vessie natatoire pour en rĂ©duire les effets
Le barotraumatisme est un phĂ©nomĂšne qui se manifeste chez les poissons capturĂ©s Ă la pĂȘche Ă de grandes profondeurs. Il engendre gĂ©nĂ©ralement un gonflement excessif de la vessie natatoire, lâexophtalmie (yeux exorbitĂ©s) ou lâexpulsion partielle des viscĂšres du poisson et peut causer la mort. Pour amĂ©liorer la survie des poissons relĂąchĂ©s, certains pĂȘcheurs pratiquent la perforation de la vessie natatoire (ou fizzing) pour en relĂącher les gaz et ensuite permettre au poisson de regagner le fond. Le prĂ©sent projet avait pour but de documenter la prĂ©valence des barotraumatismes, le taux de mortalitĂ© quâils engendrent et lâefficacitĂ© de la perforation de la vessie natatoire comme mĂ©thode dâattĂ©nuation des effets du choc baromĂ©trique. Les rĂ©sultats indiquent que, lorsque pĂȘchĂ©s Ă des profondeurs excĂ©dant 5 m, le tiers des dorĂ©s et des achigans capturĂ©s Ă la pĂȘche rĂ©crĂ©ative prĂ©sentent des symptĂŽmes de barotraumatisme et jusquâĂ 20 % des individus risquent dâen mourir. La profondeur de la capture influence positivement la prĂ©valence et la gravitĂ© des symptĂŽmes de choc baromĂ©trique. Les rĂ©sultats de la mĂ©thode de perforation de la vessie natatoire se sont avĂ©rĂ©s mitigĂ©s et suggĂšrent que lâintervention peut augmenter la survie des poissons uniquement lorsque pratiquĂ©e dans des conditions optimales, ce qui est rarement le cas en situation de pĂȘche rĂ©crĂ©ative. De plus, lâintervention sâavĂšre frĂ©quemment inefficace pour soulager les symptĂŽmes de barotraumatisme et peut engendrer des dommages et des lĂ©sions lĂ©tales Ă moyen terme. Il est donc recommandĂ© de ne pas pratiquer la perforation de la vessie natatoire, et ce, peu importe les circonstances. Des recommandations ont Ă©galement Ă©tĂ© Ă©mises pour rĂ©duire les risques de barotraumatisme et la mortalitĂ© qui en dĂ©coule
Interactions between iron and organic carbon in a sandy beach subterranean estuary
Understanding the behavior of terrestrially derived dissolved organic carbon (DOC) through subterranean estuaries (STEs) is essential for determining the carbon budget in coastal waters. However, few studies exist on the interaction of organic carbon (OC) and iron (Fe) in these dynamic systems, where fresh groundwater mixes with recirculated seawater. Here, we focused on the origin and behavior of DOC, and we quantified the relative proportion of OC trapped by reactive Fe-hydroxides along a sandy beach STE. The ÎŽ13C-DOC signal in beach groundwater seems to respond rapidly to OC inputs. Our results show a terrestrial imprint from the aquifer matrix dominated by the degradation of particulate organic carbon (POC) issue from an old soil horizon composed of terrestrial plant detritus (14C dating ~800 to 700âŻyears B.P) which is buried below the Holocene sand. Even though the system can be sporadically affected by massive inputs of marine OC, this transient marine imprint seems to be rapidly evacuated from the STE. As reported in soil and in marine mud, FeâOC trapping occurs in the sandy sediment of the STE. At the groundwaterâseawater interface, newly precipitated reactive Fe-hydroxides interact with and trap terrestrial OC independently of the DOC origin in beach groundwater. The molecular fractionation of DOC along the STE and preferential trapping of terrestrial compounds favor the in situ degradation and/or export of non-Fe-stabilized marine-derived molecules to coastal waters. These findings support the idea that the sandy beach STE acts as a transient sink for terrestrial OC at the landâsea interface and contributes to the regulation of marine vs. terrestrial carbon exports to coastal waters
PĂȘche hivernale : comparaison de lâefficaciteÌ de diffeÌrentes meÌthodes pour la capture du doreÌ et de la perchaude
Depuis le 1er avril 2017, il est interdit dâutiliser et de possĂ©der des poissons appĂąts vivants en saison hivernale. Par consĂ©quent, plusieurs adeptes de la pĂȘche sur la glace doivent adapter leur pratique. Afin de rĂ©pondre Ă leurs interrogations, une Ă©tude a Ă©tĂ© rĂ©alisĂ©e Ă lâhiver 2018. Le projet avait pour but de cibler les meilleures mĂ©thodes de pĂȘche autres que celle des poissons appĂąts vivants pour la capture du dorĂ© et de la perchaude en saison hivernale.
Pour ce faire, une sĂ©rie dâexpĂ©riences a Ă©tĂ© menĂ©e sur trois plans dâeau du sud-ouest de la province de QuĂ©bec, soit le lac Saint-Pierre, le lac Saint-Louis et le lac Champlain (baie Missisquoi). Pour deux techniques de pĂȘche, la brimbale et la dandinette, diffĂ©rents appĂąts naturels et leurres artificiels autorisĂ©s dans ces plans dâeau et disponibles dans le commerce au dĂ©tail ont Ă©tĂ© comparĂ©s dans le but dâĂ©valuer le succĂšs de pĂȘche. De façon complĂ©mentaire, la survie Ă la remise Ă lâeau a Ă©tĂ© Ă©valuĂ©e chez les dorĂ©s capturĂ©s au lac Saint-Pierre et comparĂ©e entre les mĂ©thodes de pĂȘche utilisĂ©es. Ă la brimbale, plus de la moitiĂ© des dorĂ©s ont Ă©tĂ© capturĂ©s Ă lâaide du poisson appĂąt mort congelĂ© sans traitement particulier. Ă la dandinette, pour la pĂȘche au dorĂ©, le poisson nageur Ă action verticale et la cuillĂšre, tous deux munis dâun appĂąt naturel, ont Ă©tĂ© les catĂ©gories de leurres les plus efficaces. Pour la pĂȘche Ă la perchaude, lâefficacitĂ© des leurres testĂ©s diffĂ©rait entre les deux plans dâeau visitĂ©s pour les deux techniques de pĂȘche. Au lac Champlain, les brimbales appĂątĂ©es avec des vers rouges ont Ă©tĂ© les plus efficaces, rĂ©coltant 40 % des captures, alors quâau lac Saint-Louis, les poissons appĂąts congelĂ©s sans traitement ont Ă©tĂ© les plus attractifs avec 32 % des captures. Ă la dandinette, la nymphe des glaces munie dâun asticot a Ă©tĂ© la plus efficace au lac Champlain tandis que la cuillĂšre munie dâun appĂąt naturel a Ă©tĂ© meilleure au lac Saint-Louis. Ces rĂ©sultats opposĂ©s sâexpliqueraient par le fait quâil y a une plus grande proportion de perchaudes de grande taille au lac Saint-Louis quâau lac Champlain, et que ces derniĂšres ont une alimentation davantage piscivore. Ă la dandinette, la majoritĂ© des catĂ©gories de leurres artificiels testĂ©s ont bĂ©nĂ©ficiĂ©, Ă des degrĂ©s diffĂ©rents, de lâajout dâun appĂąt naturel en termes de succĂšs de pĂȘche. Câest la cuillĂšre qui a profitĂ© le plus de cet ajout, et ce, pour la capture du dorĂ© et de la perchaude. La survie des dorĂ©s remis Ă lâeau a Ă©tĂ©, quant Ă elle, trĂšs Ă©levĂ©e (95,3 %) en pĂ©riode hivernale, et ce, peu importe la taille des poissons, la technique de capture et le type de leurre utilisĂ©. Les rĂ©sultats obtenus dans le cadre de cette Ă©tude confirment lâefficacitĂ© de plusieurs mĂ©thodes de pĂȘche en saison hivernale pour la capture du dorĂ© et de la perchaude
Factors influencing black spruce reproductive potential in the northern boreal forest of Quebec
Abstract
The reproductive ecology of the semi-serotinous species black spruce (Picea mariana (Mill.) BSP) in northern boreal forests remains poorly understood. There is a general lack of data on cone/seed production and viability as a function of biotic tree-level characteristics and abiotic variables. No studies currently exist to quantify these differences over a large gradient in temperature, elevation, and precipitation. Extensive physical, ecological, dendrometric, and reproductive data were collected from young to very old black spruce stands in northern Quebec. ANOVA and general linear mixed models were used to examine interannual cone production, and the relative importance of the biotic and abiotic explanatory factors in determining total cone production; length of the cone-bearing zone; filled seeds per cone; proportion of filled seeds; and seed viability. The results illustrate that the reproductive ecology of black spruce in northern cold forests is mainly explained by biotic variables such as age and diameter at breast height, and by abiotic variables related to temperature such as elevation, length of the growing season, and growing degree-days. Black spruce exhibits a lower reproductive potential in northern cold forests, making it possibly less resilient to increased fire frequency, particularly in unproductive and very young or very old stands.
Résumé
L'Ă©cologie de la reproduction de l'espĂšce semi-serotineuse, l'Ă©pinette noire (Picea mariana (Mill.) BSP) dans les forĂȘts borĂ©ales froides est encore peu documentĂ©e. Il existe un manque gĂ©nĂ©ral de donnĂ©es sur la production des cĂŽnes/graines et leur viabilitĂ© en fonction des caractĂ©ristiques biotiques au niveau de l'arbre et des variables abiotiques. Aucune Ă©tude nâexiste actuellement pour quantifier ces diffĂ©rences sur un large gradient de tempĂ©rature, d'altitude, et de prĂ©cipitations. De nombreuses donnĂ©es physiques, Ă©cologiques, dendromĂ©triques et reproductives ont Ă©tĂ© recueillies dans des peuplements dâĂ©pinette noire jeunes Ă trĂšs ĂągĂ©s dans le nord du QuĂ©bec. Des ANOVA et des modĂšles mixtes linĂ©aires gĂ©nĂ©raux ont Ă©tĂ© utilisĂ©s pour examiner la production annuelle de cĂŽnes et l'importance relative des facteurs explicatifs biotiques et abiotiques dans la dĂ©termination de la production totale de cĂŽnes; la longueur de la cime comportant des cĂŽnes; le nombre de graines pleines par cĂŽne; la proportion de graines pleines; et leur taux de germination. Les rĂ©sultats indiquent que l'Ă©cologie de la reproduction de l'Ă©pinette noire dans les forĂȘts borĂ©ales nordiques est expliquĂ©e par des variables biotiques telles que l'Ăąge et le DHP, et des variables abiotiques liĂ©es Ă la somme thermique rĂ©gionale telles que l'altitude, la durĂ©e de la saison de croissance, et les degrĂ©s-jours de croissance. L'Ă©pinette noire prĂ©sente un potentiel reproductif plus faible dans les forĂȘts froides du nord, ce qui la rend moins rĂ©sistante Ă l'augmentation de la frĂ©quence des feux, particuliĂšrement dans les peuplements improductifs et trĂšs jeunes ou trĂšs vieux
Increasing fire and the decline of fire adapted black spruce in the boreal forest
Intensifying wildfire activity and climate change can drive rapid forest compositional shifts. In boreal North America, black spruce shapes forest flammability and depends on fire for regeneration. This relationship has helped black spruce maintain its dominance through much of the Holocene. However, with climate change and more frequent and severe fires, shifts away from black spruce dominance to broadleaf or pine species are emerging, with implications for ecosystem functions including carbon sequestration, water and energy fluxes, and wildlife habitat. Here, we predict that such reductions in black spruce after fire may already be widespread given current trends in climate and fire. To test this, we synthesize data from 1,538 field sites across boreal North America to evaluate compositional changes in tree species following 58 recent fires (1989 to 2014). While black spruce was resilient following most fires (62%), loss of resilience was common, and spruce regeneration failed completely in 18% of 1,140 black spruce sites. In contrast, postfire regeneration never failed in forests dominated by jack pine, which also possesses an aerial seed bank, or broad-leaved trees. More complete combustion of the soil organic layer, which often occurs in better-drained landscape positions and in dryer duff, promoted compositional changes throughout boreal North America. Forests in western North America, however, were more vulnerable to change due to greater long-term climate moisture deficits. While we find considerable remaining resilience in black spruce forests, predicted increases in climate moisture deficits and fire activity will erode this resilience, pushing the system toward a tipping point that has not been crossed in several thousand years
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