44,864 research outputs found
A solar water heater for remote communities
The RADG has been developing a solar water heater suitable for use in remote areas. The original inspiration for this project was to provide hot water for remote Aboriginal communities. It was felt that a regular and plentiful supply of hot water would encourage showering and laundering and hence improve personal hygiene.
Electric, fuel burning and solar water heaters are currently used in some communities. Solar water heaters are attractive for remote areas because they stand alone i.e. they require no external fuel source. Wood has traditionally been used as a fuel by Aboriginal people, but in permanent communities the demand on this resource may have a large impact on the environment. Solar water heaters can help to reduce this demand
Unified molecular field theory of nematic, smectic-A, and smectic-C phases
A unified mean-field molecular theory of nematic (NU), smectic A (SmA), and smectic C (SmC) liquid crystal phases, composed of uniaxial nonpolar molecules, is developed taking into account the variation of all orientational and translational order parameters in these phases. Numerical results, obtained by direct global minimization of the free energy, are presented in the form of three typical phase diagrams of different topology. Temperature variation of the relevant order parameters in different sequences of phases is analyzed for various cross sections of the phase diagrams. The present model enables one to reproduce all possible sequences of phase transitions between the given phases including isotropic (Iso)-NU-SmA-SmC, Iso-NU-SmC, Iso-SmA-SmC, and Iso-SmC. The properties of the NAC point, where the NU, SmA, and SmC structures coexist, are considered in detail and the shape of the phase diagram in the vicinity of the NAC point is compared with existing experimental data
The magnetic fields of forming solar-like stars
Magnetic fields play a crucial role at all stages of the formation of low
mass stars and planetary systems. In the final stages, in particular, they
control the kinematics of in-falling gas from circumstellar discs, and the
launching and collimation of spectacular outflows. The magnetic coupling with
the disc is thought to influence the rotational evolution of the star, while
magnetised stellar winds control the braking of more evolved stars and may
influence the migration of planets. Magnetic reconnection events trigger
energetic flares which irradiate circumstellar discs with high energy particles
that influence the disc chemistry and set the initial conditions for planet
formation. However, it is only in the past few years that the current
generation of optical spectropolarimeters have allowed the magnetic fields of
forming solar-like stars to be probed in unprecedented detail. In order to do
justice to the recent extensive observational programs new theoretical models
are being developed that incorporate magnetic fields with an observed degree of
complexity. In this review we draw together disparate results from the
classical electromagnetism, molecular physics/chemistry, and the geophysics
literature, and demonstrate how they can be adapted to construct models of the
large scale magnetospheres of stars and planets. We conclude by examining how
the incorporation of multipolar magnetic fields into new theoretical models
will drive future progress in the field through the elucidation of several
observational conundrums.Comment: 55 pages, review article accepted for publication in Reports on
Progress in Physics. Astro-ph version includes additional appendice
Swarm behavior of self-propelled rods and swimming flagella
Systems of self-propelled particles are known for their tendency to aggregate
and to display swarm behavior. We investigate two model systems, self-propelled
rods interacting via volume exclusion, and sinusoidally-beating flagella
embedded in a fluid with hydrodynamic interactions. In the flagella system,
beating frequencies are Gaussian distributed with a non-zero average. These
systems are studied by Brownian-dynamics simulations and by mesoscale
hydrodynamics simulations, respectively. The clustering behavior is analyzed as
the particle density and the environmental or internal noise are varied. By
distinguishing three types of cluster-size probability density functions, we
obtain a phase diagram of different swarm behaviors. The properties of
clusters, such as their configuration, lifetime and average size are analyzed.
We find that the swarm behavior of the two systems, characterized by several
effective power laws, is very similar. However, a more careful analysis reveals
several differences. Clusters of self-propelled rods form due to partially
blocked forward motion, and are therefore typically wedge-shaped. At higher rod
density and low noise, a giant mobile cluster appears, in which most rods are
mostly oriented towards the center. In contrast, flagella become
hydrodynamically synchronized and attract each other; their clusters are
therefore more elongated. Furthermore, the lifetime of flagella clusters decays
more quickly with cluster size than of rod clusters
Forgetfulness of continuous Markovian quantum channels
The notion of forgetfulness, used in discrete quantum memory channels, is
slightly weakened in order to be applied to the case of continuous channels.
This is done in the context of quantum memory channels with Markovian noise. As
a case study, we apply the notion of weak-forgetfulness to a bosonic memory
channel with additive noise. A suitable encoding and decoding unitary
transformation allows us to unravel the effects of the memory, hence the
channel capacities can be computed using known results from the memoryless
setting.Comment: 6 pages, 2 figures, comments are welcome. Minor corrections and
acknoledgment adde
Search for the Standard Model Higgs Boson in the Diphoton Decay Channel with 4.9 fb^(-1) of pp Collision Data at âs = 7 TeV with ATLAS
A search for the standard model Higgs boson is performed in the diphoton decay channel. The data used correspond to an integrated luminosity of 4.9ââfb^(-1) collected with the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of âs = 7ââTeV. In the diphoton mass range 110â150 GeV, the largest excess with respect to the background-only hypothesis is observed at 126.5 GeV, with a local significance of 2.8 standard deviations. Taking the look-elsewhere effect into account in the range 110â150 GeV, this significance becomes 1.5 standard deviations. The standard model Higgs boson is excluded at 95% confidence level in the mass ranges of 113â115 GeV and 134.5â136 GeV
Measurement of the W âÏÎœ_Ï cross section in pp collisions at âs = 7 TeV with the ATLAS experiment
The cross section for the production of W bosons with subsequent decay WâÏÎœ_Ï is measured with the ATLAS detector at the LHC. The analysis is based on a data sample that was recorded in 2010 at a protonâproton center-of-mass energy of âs = 7TeV and corresponds to an integrated luminosity of 34 pb^(â1). The cross section is measured in a region of high detector acceptance and then extrapolated to the full phase space. The product of the total W production cross section and the WâÏÎœ_Ï branching ratio is measured to be Ï^(tot)
_(WâÏÎœÏ) = 11.1±0.3 (stat)±1.7 (syst)±0.4 (lumi) nb
Measurement of the W^±Z production cross section and limits on anomalous triple gauge couplings in protonâproton collisions at âs = 7 TeV with the ATLAS detector
This Letter presents a measurement of W^± Z production in 1.02 fb^(â1) of pp collision data at âs = 7 TeV collected by the ATLAS experiment in 2011. Doubly leptonic decay events are selected with electrons, muons and missing transverse momentum in the final state. In total 71 candidates are observed, with a background expectation of 12.1 ± 1.4(stat.)^(+4.1)_(â2.0)(syst.) events. The total cross section for W^± Z production for Z/Îł^â masses within the range 66 GeV to 116 GeV is determined to be Ï^(tot)_(WZ) = 20.5^(+3.1)_(â2.8)(stat.)^(+1.4)_(â1.3)(syst.)^(+0.9)_(â0.8)(lumi.) pb, which is consistent with the Standard Model expectation of 17.3^(+1.3) _(0.8) pb. Limits on anomalous triple gauge boson couplings are extracted
Search for a Light Higgs Boson Decaying to Long-Lived Weakly Interacting Particles in Proton-Proton Collisions at âs = 7 TeV with the ATLAS Detector
A search for the decay of a light Higgs boson (120â140 GeV) to a pair of weakly interacting, long-lived particles in 1.94ââfb^(-1) of proton-proton collisions at âs=7ââTeV recorded in 2011 by the ATLAS detector is presented. The search strategy requires that both long-lived particles decay inside the muon spectrometer. No excess of events is observed above the expected background and limits on the Higgs boson production times branching ratio to weakly interacting, long-lived particles are derived as a function of the particle proper decay length
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