29,135 research outputs found
Degrees of Freedom and Achievable Rate of Wide-Band Multi-cell Multiple Access Channels With No CSIT
This paper considers a -cell multiple access channel with inter-symbol
interference. The primary finding of this paper is that, without instantaneous
channel state information at the transmitters (CSIT), the sum
degrees-of-freedom (DoF) of the considered channel is
with when the number of users per cell is sufficiently large,
where is the ratio of the maximum channel-impulse-response (CIR) length
of desired links to that of interfering links in each cell. Our finding implies
that even without instantaneous CSIT, \textit{interference-free DoF per cell}
is achievable as approaches infinity with a sufficiently large number
of users per cell. This achievability is shown by a blind interference
management method that exploits the relativity in delay spreads between desired
and interfering links. In this method, all inter-cell-interference signals are
aligned to the same direction by using a discrete-Fourier-transform-based
precoding with cyclic prefix that only depends on the number of CIR taps. Using
this method, we also characterize the achievable sum rate of the considered
channel, in a closed-form expression.Comment: Submitted to IEEE Transactions on Communication
Supersymmetric Double Field Theory: Stringy Reformulation of Supergravity
We construct a supersymmetric extension of double field theory that realizes
the ten-dimensional Majorana-Weyl local supersymmetry. In terms of a stringy
differential geometry we proposed earlier, our action consists of five simple
terms -- two bosonic plus three fermionic -- and manifests not only
diffeomorphism and one-form gauge symmetry of B-field, but also O(10,10)
T-duality as well as a direct product of two local Lorentz symmetries, SO(1,9)
\times SO(9,1). A gauge fixing that identifies the double local Lorentz groups
reduces our action to the minimal supergravity in ten dimensions.Comment: Initally submitted to PRL on 28th November 2011. 5+4 pages (Five
pages of publication in PRD Rapid Communications plus Four pages of
Appendix). v4) Typo in Eq.(34) fixed, Erratum to be published in journal. cf.
http://www.newton.ac.uk/programmes/BSM/seminars/021611301.htm
The Historical Geography of Rice Culture in the American South.
The South Atlantic Hearth was the dominant rice producer during the colonial and antebellum periods. Rice production in the region declined after the outbreak of the Civil War, but the region kept the leading position until the 1880s. Along the Lower Mississippi River in southern Louisiana a remarkable amount of rice was produced from the antebellum period, reaching a peak in the 1890s. A major regional shift occurred when rice culture on a large-scale, commercial basis developed in southwestern Louisiana during the 1880s by transplanted Midwesterners. From there it spread into southeastern Texas during the last decade of the nineteenth century, and into the Grand Prairie during the first decade of this century. During this century, it gradually spread along the Lower Mississippi River Valley in eastern Arkansas, Mississippi Yazoo Basin, northeastern Louisiana, and southeastern Missouri. The Gulf Coast Prairies and the Lower Mississippi River Valley remain the most important two rice-growing regions in the South. Water supply and management techniques, farm machinery for rice culture, rice varieties, crop rotation methods, and other cultivation practices have all changed through time in the South, and the development of the agricultural technology for rice farming has contributed to the increasing yield of rice. Southern rice farmers have organized their rice cooperatives for rice marketing, milling, and drying and storage. They also benefited from many other organizations and institutes such as the rice experiment stations, the rice promotion organizations, the Rice Millers Association, and other governmental agencies. The role of government became remarkably active through the production control and price support system after the first Agricultural Adjustment was enacted in 1933. In this study, the historical geography of rice culture in the American South is explained in terms of economic processes, technological processes, agronomic processes, social processes, and political processes. All these processes are also related with each other. Despite the tremendous potential for rice production the future of the southern rice industry depends on various factors including agricultural technology, socio-political environment, international demand for the U.S. rice, and the relative importance of alternative crops
The Light and Period Variations of the Eclipsing Binary BX Draconis
New CCD photometric observations of BX Dra were obtained for 26 nights from
2009 April to 2010 June. The long-term photometric behaviors of the system are
presented from detailed studies of the period and light variations, based on
the historical data and our new observations. All available light curves
display total eclipses at secondary minima and inverse O'Connell effects with
Max I fainter than Max II, which are satisfactorily modeled by adding the
slightly time-varying hot spot on the primary star. A total of 87 times of
minimum light spanning over about 74 yrs, including our 22 timing measurements,
were used for ephemeris computations. Detailed analysis of the O-C diagram
showed that the orbital period has changed in combinations with an upward
parabola and a sinusoidal variation. The continuous period increase with a rate
of +5.65 \times 10^-7 d yr^-1 is consistent with that calculated from the
Wilson-Devinney synthesis code. It can be interpreted as a mass transfer from
the secondary to the primary star at a rate of 2.74 \times 10^-7 M\odot yr^-1,
which is one of the largest rates for contact systems. The most likely
explanation of the sinusoidal variation with a period of 30.2 yrs and a
semi-amplitude of 0.0062 d is a light-traveltime effect due to the existence of
a circumbinary object. We suggest that BX Dra is probably a triple system,
consisting of a primary star with a spectral type of F0, its secondary
component of spectral type F1-2, and an unseen circumbinary object with a
minimum mass of M3 = 0.23 M\odot.Comment: 24 pages, including 5 figures and 9 tables, accepted for publication
in PAS
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Cell migration directionality and speed are independently regulated by RasG and Gβ in Dictyostelium cells in electrotaxis.
Motile cells manifest increased migration speed and directionality in gradients of stimuli, including chemoattractants, electrical potential and substratum stiffness. Here, we demonstrate that Dictyostelium cells move directionally in response to an electric field (EF) with specific acceleration/deceleration kinetics of directionality and migration speed. Detailed analyses of the migration kinetics suggest that migration speed and directionality are separately regulated by Gβ and RasG, respectively, in EF-directed cell migration. Cells lacking Gβ, which is essential for all chemotactic responses in Dictyostelium, showed EF-directed cell migration with the same increase in directionality in an EF as wild-type cells. However, these cells failed to show induction of the migration speed upon EF stimulation as much as wild-type cells. Loss of RasG, a key regulator of chemoattractant-directed cell migration, resulted in almost complete loss of directionality, but similar acceleration/deceleration kinetics of migration speed as wild-type cells. These results indicate that Gβ and RasG are required for the induction of migration speed and directionality, respectively, in response to an EF, suggesting separation of migration speed and directionality even with intact feedback loops between mechanical and signaling networks
Stringy Unification of Type IIA and IIB Supergravities under N=2 D=10 Supersymmetric Double Field Theory
To the full order in fermions, we construct D=10 type II supersymmetric
double field theory. We spell the precise N=2 supersymmetry transformation
rules as for 32 supercharges. The constructed action unifies type IIA and IIB
supergravities in a manifestly covariant manner with respect to O(10,10)
T-duality and a pair of local Lorentz groups, or Spin(1,9) \times Spin(9,1),
besides the usual general covariance of supergravities or the generalized
diffeomorphism. While the theory is unique, the solutions are twofold. Type IIA
and IIB supergravities are identified as two different types of solutions
rather than two different theories.Comment: v1) 4+9 pages. v2) 1+26 pages, Unification highlighted. References
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