The baryon density at z=0.9-1.9 - Tracing the warm-hot intergalactic medium with broad Lyman alpha absorption

We present an analysis of the Lyman alpha forests of five quasar spectra in the near UV. Properties of the intergalactic medium (IGM) at an intermediate redshift interval (0.9 < z < 1.9) are studied. The amount of baryons in the diffuse photoionised IGM and the warm-hot intergalactic medium (WHIM) are traced to get constraints on the redshift evolution of the different phases of the intergalactic gas. The baryon density of the diffuse IGM is determined with photoionisation calculations under the assumption of local hydrostatic equilibrium. We assume that the gas is ionised by a metagalactic background radiation with a Haardt & Madau (2001) spectrum. The WHIM is traced with broad Lyman alpha (BLA) absorption. The properties of a number of BLA detections are studied. Under the assumption of collisional ionisation equilibrium a lower limit to the baryon density could be estimated. It is found that the diffuse photoionised IGM contains at least 25% of the total baryonic matter at redshifts 1 < z < 2. For the WHIM a lower limit of 2.4% could be determined. Furthermore the data indicates that the intergalactic gas is in a state of evolution at z=1.5. We confirm that a considerable part of the WHIM is created between z=1 and z=2.Comment: 6 pages, 1 figure, accepted for publication in A&

Representations of p-brane topological charge algebras

The known extended algebras associated with p-branes are shown to be generated as topological charge algebras of the standard p-brane actions. A representation of the charges in terms of superspace forms is constructed. The charges are shown to be the same in standard/extended superspace formulations of the action.Comment: 22 pages. Typos fixed, refs added. Minor additions to comments sectio

Aging and memory properties of topologically frustrated magnets

The model 2d kagome system (H3O)Fe3(SO4)2(OH)6 and the 3d pyrochlore Y2Mo2O7 are two well characterized examples of low-disordered frustrated antiferromagnets which rather then condensing into spin liquid have been found to undergo a freezing transition with spin glass-like properties. We explore more deeply the comparison of their properties with those of spin glasses, by the study of characteristic rejuvenation and memory effects in the non-stationary susceptibility. While the pyrochlore shows clear evidence for these non-trivial effects, implying temperature selective aging, that is characteristic of a wide hierarchical distribution of equilibration processes, the kagome system does n not show clearly these effects. Rather, it seems to evolve towards the same final state independently of temperature.Comment: submitted for the proceedings of the 46th MMM conference (Seattle, 2001

Static Critical Behavior of the Spin-Freezing Transition in the Geometrically Frustrated Pyrochlore Antiferromagnet Y2Mo2O7

Some frustrated pyrochlore antiferromagnets, such as Y2Mo2O7, show a spin-freezing transition and magnetic irreversibilities below a temperature Tf similar to what is observed nonlinear magnetization measurements on Y2Mo2O7 that provide strong evidence that there is an underlying thermodynamic phase transition at Tf, which is characterized by critical exponents \gamma \approx 2.8 and \beta \approx 0.8. These values are typical of those found in random spin glasses, despite the fact that the level of random disorder in Y2Mo2O7 is immeasurably small.Comment: Latex file, calls for 4 encapsulated postscript figures (included). Submitted to Phys. Rev. Letters

Molecular quantum cellular automata cell design trade-offs: latching vs. power dissipation.

The use of molecules to enact quantum cellular automata (QCA) cells has been proposed as a new way for performing electronic logic operations at sub-nm dimensions. A key question that arises concerns whether chemical or physical processes are to be exploited. The use of chemical reactions allows the state of a switch element to be latched in molecular form, making the output of a cell independent of its inputs, but costs energy to do the reaction. Alternatively, if purely electronic polarization is manipulated then no internal latching occurs, but no power is dissipated provided the fields from the inputs change slowly compared to the molecular response times. How these scenarios pan out is discussed by considering calculated properties of the 1,4-diallylbutane cation, a species often used as a paradigm for molecular electronic switching. Utilized are results from different calculation approaches that depict the ion either as a charge-localized mixed-valence compound functioning as a bistable switch, or else as an extremely polarizable molecule with a delocalized electronic structure. Practical schemes for using molecular cells in QCA and other devices emerge

On the Metallicity-Color Relations and Bimodal Color Distributions in Extragalactic Globular Cluster Systems

We perform a series of numerical experiments to study how the nonlinear metallicity--color relations predicted by different stellar population models affect the color distributions observed in extragalactic globular cluster systems. % We present simulations in the $UBVRIJHK$ bandpasses based on five different sets of simple stellar population (SSP) models. The presence of photometric scatter in the colors is included as well. % We find that unimodal metallicity distributions frequently ``project'' into bimodal color distributions. The likelihood of this effect depends on both the mean and dispersion of the metallicity distribution, as well as of course on the SSP model used for the transformation. % Adopting the Teramo-SPoT SSP models for reference, we find that optical--to--near-IR colors should be favored with respect to other colors to avoid the bias effect in globular cluster color distributions discussed by \citet{yoon06}. In particular, colors such as \vh\ or \vk are more robust against nonlinearity of the metallicity--color relation, and an observed bimodal distribution in such colors is more likely to indicate a true underlying bimodal metallicity distribution. Similar conclusions come from the simulations based on different SSP models, although we also identify exceptions to this result.Comment: ApJ accepte

Reindeer and caribou (Rangifer tarandus) response towards human activities

We address the question of how human activities and infrastructure influence reindeer/caribou&rsquo;s (Rangifer tarandus) behaviour and habitat use and review studies based on current methodologies. Anthropogenic activities have a direct affect on Rangifer behaviour through the senses hearing, sight and smell, and all of these are important tools for behavioural risk assessment. Short term indirect responses, such as habituation, sensitisation, avoidance, and displacement, develop through neutral, positive or negative associations towards stimulus in terms of Rangifer&rsquo;s ability to experience, learn, and remember. Long term behavioural responses develop through interaction with predators and, for reindeer, also domestication. A survey of the literature dealing with behavioural studies reveals that although Rangifer in most cases retreat from anthropogenic activities, comfort distances (i.e. distances beyond which animal behaviour or activity are not influenced) are relatively short. In most cases, energetic implications appear moderate and small compared to other natural, biotic influences such as disturbance (and death) caused by insect and/or predator harassment. Unless obstructing access, physical constructions of various kinds apparently have limited effects on Rangifer behaviour or habitat use. On the other hand, constructions that do obstruct or limit access and recreational or other motorized and non-motorized activities appear to have stronger impacts on avoidance and redistribution of Rangifer. Behavioural effects that might decrease survival and reproduction include retreat from favourable habitat near disturbance sources and reduction of time spent feeding with resulting energy depletion over time. Rangifer habitat use, habitat avoidance, and feeding preferences are governed by a complexity of natural interacting factors. Domestication, habituation and sensitisation are essential in shaping Rangifer&rsquo;s adaptability, and should be included in future studies on reindeer and caribou responses towards various anthropogenic activities. Although cumulative effects from human activities are likely, it remains difficult to separate these from natural variations in Rangifer habitat use and demography. Habitat avoidance towards various human infrastructures and activities is reported, but most studies reporting relatively far (4-25 km) avoidance distances relied on measurements of range properties and animal distribution recorded on 1-2 days annually in winter to induce a potential response from the animals and lack important environmental variables and/or alternative hypothesises. This methodology should be improved in order to enable identification of correlation versus causation. Studies relying on animal behaviour measurements can more correctly identify and test responses to various stimuli while also controlling for degree of domestication and other various environmental variables, but only in a limited time and spatial scale. Furthermore, such studies may not necessarily capture potential population consequences from disturbances. Thus, there are important weaknesses in the two leading methodologies (measuring animal behaviour and indirectly mapping regional/population movements and habitat use through measurements of range properties). To best study Rangifer&rsquo;s responses towards anthropogenic infrastructure and activities, we propose that the two methodologies be combined and supplied with modern GPS/telemetry.Abstract in Norwegian / Sammendrag:Rein og caribous reaksjon p&aring; forskjellige menneskelige aktiviteter og installasjoner Vi adresserer sp&oslash;rsm&aring;let om hvordan menneskelig aktivitet og infrastruktur p&aring;virker rein/caribous (Rangifer tarandus) atferd og omr&aring;debruk og gjennomg&aring;r publiserte arbeider basert p&aring; aktuelle metoder. Antropogene aktiviteter har direkte effekt p&aring; reinens atferd via h&oslash;rsel, syn og lukt; alle er viktige for deres risikovurdering. Kortsiktige indirekte reaksjonsm&oslash;nstre, slik som habituering, sensitivisering, unnvikelse og fortrengning utvikles gjennom n&oslash;ytrale, positive eller negative opplevelser av stimuli i henhold til erfaring, l&aelig;ring og hukommelse. Utviklingen av permanente atferdsm&oslash;nstre skjer ved samvirke med predatorer og for reinens del, ogs&aring; ved domestisering. En litteraturoversikt om atferdsstudier viser at selv om Rangifer i de fleste tilfeller unnviker antropogene virksomheter, s&aring; er de avstander dyrene velger &aring; ha mellom seg og infrastruktur uten at normalatferden endres, relativt korte. De energimessige implikasjonene er ogs&aring; beskjedne sammenlignet med virkningen av naturlige stressfaktorer s&aring; som forstyrrelser (og d&oslash;d) for&aring;rsaket av insekter og predatorer. Fysiske installasjoner av ulik art har ogs&aring; begrenset effekt med mindre de fysisk hindrer Rangifers omr&aring;debruk. P&aring; den annen side vil fysiske installasjoner, som hindrer eller begrenser bruken av omr&aring;der, og trafikk, b&aring;de fottrafikk og trafikk med motorkj&oslash;ret&oslash;y, kunne ha sterkere virkning p&aring; unnvikelsesatferd og omr&aring;debruk. Atferdsmessige effekter som kan redusere overlevelse og reproduksjon omfatter unnvikelse fra beiteomr&aring;der n&aelig;r forstyrrelseskilder. For Rangifer er det negative resultatet av dette &oslash;ket aktivitet, redusert beitetid og nedbygging av energireserver. Rangifers omr&aring;debruk, unnvikelsesatferd og n&aelig;ringspreferanser bestemmes ut fra et kompleks av naturlige og gjensidig p&aring;virkende faktorer. Domestisering, habituering og sensitivisering som er sentrale begrep i utformningen av Rangifers tilpasningsevne, b&oslash;r inkluderes i fremtidige studier av rein og caribous reaksjon p&aring; antropogene aktiviteter. Selv om en kumulativ atferdseffekt av menneskelige aktiviteter er mulig, er det vanskelig &aring; skille slike fra naturlige variasjoner som f&oslash;lge av variasjoner i omr&aring;debruk og bestandsdynamiske forhold. Habitatunnvikelse som f&oslash;lge av menneskelig p&aring;virkning er rapportert. De fleste studiene som rapporterer relativt lange unnvikelsesavstander (4-25 km) er imidlertid basert p&aring; m&aring;linger av beiteslitasje og lokalisering av dyr registrert i l&oslash;pet av 1-2 dager &aring;rlig i l&oslash;pet av vinteren og mangler viktige milj&oslash;parametere og/eller alternative hypoteser. Denne metoden b&oslash;r forbedres for &aring; kunne skille mellom korrelasjon og kausalitet. M&aring;linger av atferd gj&oslash;r mulig en mer korrekt testing av Rangifers reaksjon p&aring; ulike antropogene stimuli samtidig som man kontrollerer for graden av domestisering og forskjellige milj&oslash;faktorer. Atferdsstudiene avgrenses imidlertid i b&aring;de tid og rom og vil vanligvis ikke fange opp eventuelle bestandsdynamiske konsekvenser av forstyrrelser. Det hefter f&oslash;lgelig svakheter ved begge de to dominerende metodene som i dag anvendes; m&aring;ling av atferd og bestandsfordeling og indirekte kartlegging av omr&aring;debruk ved m&aring;ling av beiteslitasje. For &aring; oppn&aring; en bedre studiedesign for m&aring;ling av Rangifers reaksjon p&aring; antropogen infrastruktur og tilknyttede aktiviteter foresl&aring;r vi at de to metodene kombineres og suppleres med GPS/telemetri teknologi

2016 Nebraska Water Leaders Academy - Final Report

The effective management of Nebraska’s water resources is evermore challenged by variations in weather, climate, technology, socioeconomic policies, and regulation. Anthropogenic climate change, declining water tables and stream flows, increasing demands on freshwater, aging water infrastructure, fiscal constraints, and impacts on aquatic organisms are particularly imminent challenges in Nebraska and around the world (Pahl-Wostl et al., 2013; Pittock et al., 2008; USACE, 2010). Sustaining freshwater ecosystem services in the face of emerging environmental threats presents an immense societal dilemma worldwide (Pittock et al., 2013; Rockström et al., 2009, Millenium Ecosystem Assessment, 2005). The rapidly changing conditions of water resources in Nebraska demands knowledgeable and skilled leaders (Burbach, et al., 2015; Lincklaen Arriëns & When de Montalvo, 2013; Morton & Brown, 2011). McIntosh and Taylor (2013) assert that in order to meet future water challenges, “leadership is needed to initiate and drive change, enable innovation (both incremental and radical), build shared visions for a more sustainable water future, and deliver these visions through aligning resources and building commitment to collective success” (p. 46). Building leadership capacity is required to drive the necessary change (Brasier et al., 2011; Morton et al., 2011; Pahl-Wostl et al., 2011; Redekop, 2010; Taylor et al., 2012). Recognizing this critical need for future leaders in water resources, the Nebraska State Irrigation Associatio

Solar-Like Cycle in Asymptotic Giant Branch Stars

I propose that the mechanism behind the formation of concentric semi-periodic shells found in several planetary nebulae (PNs) and proto-PNs, and around one asymptotic giant branch (AGB) star, is a solar-like magnetic activity cycle in the progenitor AGB stars. The time intervals between consecutive ejection events is about 200-1,000 years, which is assumed to be the cycle period (the full magnetic cycle can be twice as long, as is the 22-year period in the sun). The magnetic field has no dynamical effects; it regulates the mass loss rate by the formation of magnetic cool spots. The enhanced magnetic activity at the cycle maximum results in more magnetic cool spots, which facilitate the formation of dust, hence increasing the mass loss rate. The strong magnetic activity implies that the AGB star is spun up by a companion, via a tidal or common envelope interaction. The strong interaction with a stellar companion explains the observations that the concentric semi-periodic shells are found mainly in bipolar PNs.Comment: 10 pages, submitted to Ap

Order induced by dipolar interactions in a geometrically frustrated antiferromagnet

We study the classical Heisenberg model for spins on a pyrochlore lattice interacting via long range dipole-dipole forces and nearest neighbor exchange. Antiferromagnetic exchange alone is known not to induce ordering in this system. We analyze low temperature order resulting from the combined interactions, both by using a mean-field approach and by examining the energy cost of fluctuations about an ordered state. We discuss behavior as a function of the ratio of the dipolar and exchange interaction strengths and find two types of ordered phase. We relate our results to the recent experimental work and reproduce and extend the theoretical calculations on the pyrochlore compound, Gd$_2$Ti$_2$O$_7$, by Raju \textit{et al.}, Phys. Rev. B {\bf 59}, 14489 (1999).Comment: 5 pages, 5 figures, AMSLaTe