4,819 research outputs found
Mitigating the impact of swimming pools on domestic water demand
South Africa is a water-scarce country where the sustainable provision of water to its citizens is one of the most significant challenges faced. A recent study in Cape Town, South Africa, investigated the impact of residential swimming pools on household water demand and found that, on average, the presence of a swimming pool increased water demand by 8.85 kℓ/ month or 37.36%. Should cities in South Africa wish to develop in a water sensitive manner – where water is treated as a scarce resource with economic value in all its competing uses – it will be vital to understand the impact of swimming pools on residential water demand. Should there be a significant increase in water demand attributable to the presence of a swimming pool on a property, it would highlight the need to consider whether it is acceptable for properties to use municipal water to fill them or top them up – especially in water-scarce/stressed areas. This paper describes a study undertaken in the Liesbeek River catchment, Cape Town, to investigate the impact that swimming pools have on domestic water demand. The results support the contention that properties with swimming pools use significantly more water than those without. This study estimated the additional demand resulting from swimming pools at between 2.2–2.4 kℓ/month or 7–8% of total water demand. The data also indicate that the presence of a swimming pool correlates with a higher indoor demand. The study shows the need to reduce the impact of swimming pools. This could include: pool covers to reduce evaporation, the recycling of backwash water, the use of rainwater to top up swimming pools, water use surcharges and, finally, appropriate regulation and enforcement to prevent the use of municipal water in swimming pools – especially during droughts.Keywords: urban water management, swimming pools, water demand managemen
Gauss Sums and Quantum Mechanics
By adapting Feynman's sum over paths method to a quantum mechanical system
whose phase space is a torus, a new proof of the Landsberg-Schaar identity for
quadratic Gauss sums is given. In contrast to existing non-elementary proofs,
which use infinite sums and a limiting process or contour integration, only
finite sums are involved. The toroidal nature of the classical phase space
leads to discrete position and momentum, and hence discrete time. The
corresponding `path integrals' are finite sums whose normalisations are derived
and which are shown to intertwine cyclicity and discreteness to give a finite
version of Kelvin's method of images.Comment: 14 pages, LaTe
Influence of the r-mode instability on hypercritically accreting neutron stars
We have investigated an influence of the r-mode instability on
hypercritically accreting () neutron stars in
close binary systems during their common envelope phases based on the scenario
proposed by Bethe et al. \shortcite{bethe-brown-lee}. On the one hand neutron
stars are heated by the accreted matter at the stellar surface, but on the
other hand they are also cooled down by the neutrino radiation. At the same
time, the accreted matter transports its angular momentum and mass to the star.
We have studied the evolution of the stellar mass, temperature and rotational
frequency.
The gravitational-wave-driven instability of the r-mode oscillation strongly
suppresses spinning-up of the star, whose final rotational frequency is well
below the mass-shedding limit, typically as small as 10% of that of the
mass-shedding state. On a very short time scale the rotational frequency tends
to approach a certain constant value and saturates there as far as the amount
of the accreted mass does not exceed a certain limit to collapse to a black
hole. This implies that the similar mechanism of gravitational radiation as the
so-called Wagoner star may work in this process. The star is spun up by
accretion until the angular momentum loss by gravitational radiation balances
the accretion torque. The time-integrated dimensionless strain of the radiated
gravitational wave may be large enough to be detectable by the gravitational
wave detectors such as LIGO II.Comment: 6 pages, 3 figure
Optical spectra of the heavy fermion uniaxial ferromagnet UGe
We report a detailed study of UGe single crystals using infrared
reflectivity and spectroscopic ellipsometry. The optical conductivity suggests
the presence of a low frequency interband transition and a narrow free-carrier
response with strong frequency dependence of the scattering rate and effective
mass. We observe sharp changes in the low frequency mass and scattering rate
below the upper ferromagnetic transition . The characteristic
changes are exhibited most strongly at an energy scale of around 12 meV (100
cm). They recover their unrenormalized value above and for 40 meV. In contrast no sign of an anomaly is seen at the lower transition
temperature of unknown nature 30 K, observed in transport and
thermodynamic experiments. In the ferromagnetic state we find signatures of a
strong coupling to the longitudinal magnetic excitations that have been
proposed to mediate unconventional superconductivity in this compound
Cyclic Di-GMP-Mediated Repression of Swarming Motility by Pseudomonas aeruginosa PA14 Requires the MotAB Stator
The second messenger cyclic diguanylate (c-di-GMP) plays a critical role in the regulation of motility. In Pseudomonas aeruginosa PA14, c-di-GMP inversely controls biofilm formation and surface swarming motility, with high levels of this dinucleotide signal stimulating biofilm formation and repressing swarming. P. aeruginosa encodes two stator complexes, MotAB and MotCD, that participate in the function of its single polar flagellum. Here we show that the repression of swarming motility requires a functional MotAB stator complex. Mutating the motAB genes restores swarming motility to a strain with artificially elevated levels of c-di-GMP as well as stimulates swarming in the wild-type strain, while overexpression of MotA from a plasmid represses swarming motility. Using point mutations in MotA and the FliG rotor protein of the motor supports the conclusion that MotA-FliG interactions are critical for c-di-GMP-mediated swarming inhibition. Finally, we show that high c-di-GMP levels affect the localization of a green fluorescent protein (GFP)-MotD fusion, indicating a mechanism whereby this second messenger has an impact on MotCD function. We propose that when c-di-GMP level is high, the MotAB stator can displace MotCD from the motor, thereby affecting motor function. Our data suggest a newly identified means of c-di-GMP-mediated control of surface motility, perhaps conserved among Pseudomonas, Xanthomonas, and other organisms that encode two stator systems
Possible Z2 phase and spin-charge separation in electron doped cuprate superconductors
The SU(2) slave-boson mean-field theory for the tt'J model is analyzed. The
role of next-nearest-neighbor hopping t' on the phase-diagram is studied. We
find a pseudogap phase in hole-doped materials (where t'<0). The pseudo-gap
phase is a U(1) spin liquid (the staggered-flux phase) with a U(1) gauge
interaction and no fractionalization. This agrees with experiments on hole
doped samples. The same calculation also indicates that a positive t' favors a
Z2 state with true spin-charge separation. The Z2 state that exists when t' >
0.5J can be a candidate for the pseudo-gap phase of electron-doped cuprates (if
such a phase exists). The experimental situation in electron-doped materials is
also addressed.Comment: 6 pages, 2 figures, RevTeX4. Homepage http://dao.mit.edu/~wen
Nonmonotonic d_{x^2-y^2} Superconducting Order Parameter in Nd_{2-x}Ce_xCuO_4
Low energy polarized electronic Raman scattering of the electron doped
superconductor Nd_1.85Ce_0.15CuO_4 (T_c=22 K) has revealed a nonmonotonic
d_{x^2-y^2} superconducting order parameter. It has a maximum gap of 4.4 k_BT_c
at Fermi surface intersections with antiferromagnetic Brillouin zone (the ``hot
spots'') and a smaller gap of 3.3 k_BT_c at fermionic Brillouin zone
boundaries. The gap enhancement in the vicinity of the ``hot spots'' emphasizes
role of antiferromagnetic fluctuations and similarity in the origin of
superconductivity for electron- and hole-doped cuprates.Comment: 4 pages, 4 figure
- …