6,530 research outputs found

### Is Sustainable Development of Deserts Feasible?

Hot deserts that presently cover about one-fifth of the land area of our planet are rapidly devouring more and more arable lands mostly due to anthropogenic causes. We propose an interdisciplinary approach to revitalizing and commercializing hot deserts, which is based on systems thinking and Russian and NASA space technology experience in designing life-support systems for long-duration flights. We formulate ten principles for the design of sustainable life support systems in deserts, which can make the development of the deserts feasible. It is discussed how the principles can be employed to design and operate desert’s eco-industrial parks with greenhouses in which the transpired and evaporated moisture is collected and condensed. The potential benefits of setting up the eco-industrial parks in deserts include the slowdown and eventual reversal of the desertification trend, the migration of many industrial production facilities from mild-climate regions to deserts, the increased availability of potable water and food in deserts, the development of poor African countries, and the emergence of new investment markets

### BRST Properties of New Superstring States

Brane-like states are defined by physical vertex operators in NSR superstring
theory, existing at nonzero pictures only. These states exist both in open and
closed string theories, in the NS and NS-NS sectors respectively. In this paper
we present a detailed analysis of their BRST properties, giving a proof that
these vertex operators are physical, i.e. BRST invariant and BRST non-trivial.Comment: 25 pages, harvmac.te

### Fluid Dynamics of NSR Strings

We show that the renormalization group flows of the massless superstring
modes in the presence of fluctuating D-branes satisfy the equations of fluid
dynamics.In particular, we show that the D-brane's U(1) field is related to the
velocity function in the Navier-Stokes equation while the dilaton plays the
role of the passive scalar advected by the turbulent flow. This leads us to
suggest a possible isomorphism between the off-shell superstring theory in the
presence of fluctuating branes and the fluid mechanical degrees of freedom.Comment: 24 pages Dedicated to the memory of Ian Koga

### Electric charge in the field of a magnetic event in three-dimensional spacetime

We analyze the motion of an electric charge in the field of a magnetically
charged event in three-dimensional spacetime. We start by exhibiting a first
integral of the equations of motion in terms of the three conserved components
of the spacetime angular momentum, and then proceed numerically. After crossing
the light cone of the event, an electric charge initially at rest starts
rotating and slowing down. There are two lengths appearing in the problem: (i)
the characteristic length $\frac{q g}{2 \pi m}$, where $q$ and $m$ are the
electric charge and mass of the particle, and $g$ is the magnetic charge of the
event; and (ii) the spacetime impact parameter $r_0$. For $r_0 \gg \frac{q g}{2
\pi m}$, after a time of order $r_0$, the particle makes sharply a quarter of a
turn and comes to rest at the same spatial position at which the event happened
in the past. This jump is the main signature of the presence of the magnetic
event as felt by an electric charge. A derivation of the expression for the
angular momentum that uses Noether's theorem in the magnetic representation is
given in the Appendix.Comment: Version to appear in Phys. Rev.

### A Quality and Cost Approach for Comparison of Small-World Networks

We propose an approach based on analysis of cost-quality tradeoffs for
comparison of efficiency of various algorithms for small-world network
construction. A number of both known in the literature and original algorithms
for complex small-world networks construction are shortly reviewed and
compared. The networks constructed on the basis of these algorithms have basic
structure of 1D regular lattice with additional shortcuts providing the
small-world properties. It is shown that networks proposed in this work have
the best cost-quality ratio in the considered class.Comment: 27 pages, 16 figures, 1 tabl

### Extra $Z$ bosons and low-energy tests of unification

If there is an extra U(1) gauge symmetry broken at low energies, then it may
be possible from the charges of the known quarks and leptons under this U(1) to
make inferences about how much gauge unification occurs at high scales and
about the unification group. (For instance, there are certain observed
properties of an extra $U(1)'$ that would be inconsistent with unification in
four dimensions at high scales.) A general analysis is presented. Two criteria
used in this analysis are (1) the degree to which the generator of the extra
U(1) mixes with hypercharge, and (2) the ratio of the extra U(1) charge of the
"10" and the "$\bar{5}$" of quarks and leptons.Comment: 27 pages, LaTex, no figures. Changed content. References added. Typos
correcte

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