3,967 research outputs found
Two-Twistor Space, Commuting Composite Minkowski Coordinates and Particle Dynamics
We employ the modification of the basic Penrose formula in twistor theory,
which allows to introduce commuting composite space-time coordinates. It
appears that in the course of such modification the internal symmetry SU(2) of
two-twistor system is broken to U(1). We consider the symplectic form on
two-twistor space, permitting to interpret its 16 real components as a
phase-space. After a suitable change of variables such a two-twistor phase
space is split into three mutually commuting parts, describing respectively the
standard relativistic phase space (8 degrees of freedom), the spin sector (6
degrees of freedom) and the canonical pair angle-charge describing the electric
charge sector (2 degrees of freedom). We obtain a geometric framework providing
a twistor-inspired 18-dimensional extended relativistic phase space
. In such a space we propose the action only with first class
constraints, describing the relativistic particle characterized by mass, spin
and electric charge.Comment: LaTeX 2e, 14 pages. To be published in the Proceedings of XIX-th Max
Born Symposium "Fundamental Interactions and Twistor-Like Methods", September
2004, American Institute of Physics, Proceedings Serie
Helminth species richness in wild wood mice, Apodemus sylvaticus, is enhanced by the presence of the intestinal nematode Heligmosomoides polygyrus
We analysed 3 independently collected datasets of fully censused helminth burdens in wood mice, Apodemus sylvaticus,
testing the a priori hypothesis of Behnke et al. (2005) that the presence of the intestinal nematode Heligmosomoides polygyrus
predisposes wood mice to carrying other species of helminths. In Portugal, mice carrying H. polygyrus showed a higher
prevalence of other helminths but the magnitude of the effect was seasonal. In Egham, mice with H. polygyrus showed a
higher prevalence of other helminth species, not confounded by other factors. In Malham Tarn, mice carrying H. polygyrus
were more likely to be infected with other species, but only among older mice. Allowing for other factors, heavy residual
H. polygyrus infections carried more species of other helminths in both the Portugal and Egham data; species richness in
Malham was too low to conduct a similar analysis, but as H. polygyrus worm burdens increased, so the prevalence of other
helminths also increased. Our results support those of Behnke et al. (2005), providing firm evidence that at the level
of species richness a highly predictable element of co-infections in wood mice has now been defined: infection with
H. polygyrus has detectable consequences for the susceptibility of wood mice to other intestinal helminth species
Quantum computation with phase drift errors
We present results of numerical simulations of the evolution of an ion trap
quantum computer made out of 18 ions which are subject to a sequence of nearly
15000 laser pulses in order to find the prime factors of N=15. We analyze the
effect of random and systematic phase drift errors arising from inaccuracies in
the laser pulses which induce over (under) rotation of the quantum state.
Simple analytic estimates of the tolerance for the quality of driving pulses
are presented. We examine the use of watchdog stabilization to partially
correct phase drift errors concluding that, in the regime investigated, it is
rather inefficient.Comment: 5 pages, RevTex, 2 figure
Non-conventional water resources in coastal areas : a review on the use of reclaimed water
In an era of increasing contest for limited water resources a wise joint management of conventional and non-conventional water resources must be considered. Water scarcity aggravates in coastal zones which are often characterised by high population density, intense economic activity and tourism meaning heavy seasonal water demands. The relationships between sea and land water can also compromise the quality of available freshwater. In this context, the use of non-conventional water increases the availability of water supplies. Non-conventional water resources of lower quality could be directed to meet several needs (like watering lawns, washing cars, flushing toilets and cooling systems, among others). Therefore, significantly more potable water would be available to meet human demand for safe water
A quantum gate array can be programmed to evaluate the expectation value of any operator
A programmable gate array is a circuit whose action is controlled by input
data. In this letter we describe a special--purpose quantum circuit that can be
programmed to evaluate the expectation value of any operator acting on a
space of states of dimensions. The circuit has a program register whose
state encodes the operator whose expectation value is to be
evaluated. The method requires knowledge of the expansion of in a basis of
the space of operators. We discuss some applications of this circuit and its
relation to known instances of quantum state tomography.Comment: 4 pages, 3 figures include
Distribution of lipid biomarkers and carbon isotope fractionation in contrasting trophic environments of the South East Pacific
The distribution of lipid biomarkers and their stable carbon isotope composition was investigated on suspended particles from different contrasting trophic environments at six sites in the South East Pacific. High algal biomass with diatom-related lipids (24-methylcholesta-5,24(28)-dien-3&beta;-ol, C<sub>25</sub> HBI alkenes, C<sub>16:4</sub> FA, C<sub>20:5</sub> FA) was characteristic in the upwelling zone, whereas haptophyte lipids (long-chain (C<sub>37</sub>-C<sub>39</sub>) unsaturated ketones) were proportionally most abundant in the nutrient-poor settings of the centre of the South Pacific Gyre and on its easter edge. The dinoflagellate–sterol, 4&alpha;-23,24-trimethylcholest-22(<i>E</i>)-en-3&beta;-ol, was a minor contributor in all of the studied area and the cyanobacteria-hydrocarbon, C<sub>17</sub><i>n</i>-alkane, was at maximum in the high nutrient low chlorophyll regime of the subequatorial waters near the Marquesas archipelago. <br><br> The taxonomic and spatial variability of the relationships between carbon photosynthetic fractionation and environmental conditions for four specific algal taxa (diatoms, haptophytes, dinoflagellates and cyanobacteria) was also investigated. The carbon isotope fractionation factor (&epsilon;<sub>p</sub>) of the 24-methylcholesta-5,24(28)-dien-3&beta;-ol diatom marker, varied over a range of 16% along the different trophic systems. In contrast, &epsilon;<sub>p</sub> of dinoflagellate, cyanobacteria and alkenone markers varied only by 7–10&permil;. The low fractionation factors and small variations between the different phytoplankton markers measured in the upwelling area likely reveals uniformly high specific growth rates within the four phytoplankton taxa, and/or that transport of inorganic carbon into phytoplankton cells may not only occur by diffusion but also by other carbon concentrating mechanisms (CCM). In contrast, in the oligotrophic zone, i.e. gyre and eastgyre, relatively high &epsilon;<sub>p</sub> values, especially for the diatom marker, indicate diffusive CO<sub>2</sub> uptake by the eukaryotic phytoplankton. At these nutrient-poor sites, the lower &epsilon;<sub>p</sub> values for haptophytes, dinoflagellates and cyanobacteria indicate higher growth rates or major differences on the carbon uptake mechanisms compared to diatoms
Vertical flux and microplankton assemblages in the Gulf of Liions during spring 1990
A vertical flux pulse related to spring phytoplankton development was recorded ·by moored sediment traps at 42°N 06°E in the Gulf of Lions. May 1990 trap samples from 200m to
2000m depth were comprised of freshly produced organic matter and selected microplankton species from the overlaying water column. This vertical flux event was transmitted to the deep sea floor with a high particle sinking velocity
of >140 m day-1. Maximal vertical fluxes of 35 mg C m-2 day-1 and 1.2 mg chl.a m-2 day-1 recorded during this event are low compared to the exports from collapsing spring blooms at higher latitudes but demonstrate that particle production and degradation within the spring pelagic system were not in balance
Quantum repeaters based on entanglement purification
We study the use of entanglement purification for quantum communication over
long distances. For distances much longer than the coherence length of a
corresponding noisy quantum channel, the fidelity of transmission is usually so
low that standard purification methods are not applicable. It is however
possible to divide the channel into shorter segments that are purified
separately and then connected by the method of entanglement swapping. This
method can be much more efficient than schemes based on quantum error
correction, as it makes explicit use of two-way classical communication. An
important question is how the noise, introduced by imperfect local operations
(that constitute the protocols of purification and the entanglement swapping),
accumulates in such a compound channel, and how it can be kept below a certain
noise level. To treat this problem, we first study the applicability and the
efficiency of entanglement purification protocols in the situation of imperfect
local operations. We then present a scheme that allows entanglement
purification over arbitrary long channels and tolerates errors on the per-cent
level. It requires a polynomial overhead in time, and an overhead in local
resources that grows only logarithmically with the length of the channel.Comment: 19 pages, 16 figure
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