49,751 research outputs found
Composite CDMA - A statistical mechanics analysis
Get PDFCode Division Multiple Access (CDMA) in which the spreading code assignment
to users contains a random element has recently become a cornerstone of CDMA
research. The random element in the construction is particular attractive as it
provides robustness and flexibility in utilising multi-access channels, whilst
not making significant sacrifices in terms of transmission power. Random codes
are generated from some ensemble, here we consider the possibility of combining
two standard paradigms, sparsely and densely spread codes, in a single
composite code ensemble. The composite code analysis includes a replica
symmetric calculation of performance in the large system limit, and
investigation of finite systems through a composite belief propagation
algorithm. A variety of codes are examined with a focus on the high
multi-access interference regime. In both the large size limit and finite
systems we demonstrate scenarios in which the composite code has typical
performance exceeding sparse and dense codes at equivalent signal to noise
ratio.Comment: 23 pages, 11 figures, Sigma Phi 2008 conference submission -
submitted to J.Stat.Mec
The Witt Ring of a Curve with Good Reduction over a Non-dyadic Local Field
Full text linkIn this work, we present a generalization to varieties and sheaves of the
fundamental ideal of the Witt ring of a field by defining a sheaf of
fundamental ideals and a sheaf of Witt rings in the
obvious way. The Milnor conjecture then relates the associated graded of
to Milnor K-theory and so allows the classical invariants of a
bilinear space over a field to be extended to our setting using \'etale
cohomology. As an application of these results, we calculate the Witt ring of a
smooth curve with good reduction over a non-dyadic local field
September 11: Symbolism And Responses To 9/11
Get PDFProfessors Hopkins and Hopkins review the impact of 9/11 as a symbol in American politics. Following the terrorist attacks, 9/11 became a simple reference condensing wide-ranging events and emotions. Various interpretations emerged about what caused 9/11 and enabled the attacks. The authors claim that 9/11 allowed US leaders to pursue certain policy prescriptions that otherwise would have been blocked. Among four possible prescriptions for responding to the attacks, the Bush administration chose a praetorian policy of preventive war, with Iraq as its first example. In the authors’ view, by pursuing an expansive but highly militarized response, the US has overlooked the need to alleviate the conditions that made 9/11 possible. The authors recommend that the US, as part of a multilateral effort, allocate major resources to expanding global public goods, including measures that strengthen barriers to proliferation, enhance fighting of global crime, and reduce incentives for terrorism, especially ones arising in failing states where distorted education and weak protection of human rights encourage organized terrorism
Assessment of recent eastern oyster (Crassostrea virginica) reef restoration projects in the Great Bay Estuary, New Hampshire: Planning for the future
Get PDFCurrent oyster populations in New Hampshire total less than 10% of what they were in the 1980s, and the causal factors for the declines include disease, sedimentation, and human harvest. The two major results from a population ecology perspective have been dramatic losses of oyster shell (the major substrate on which oyster larvae typically settle) as well as juvenile annual recruitment to the remaining reefs. Experimental scale oyster restoration projects addressing these two limitations (substrate and natural recruitment) were initiated in the state in the early 2000s by scientists at the University of New Hampshire (UNH). Since the mid-2000s, the focus has been on full restoration-scale projects, and beginning in 2009 most projects have been collaborative efforts by UNH and The Nature Conservancy (TNC). The present study assessed nine recent collaborative efforts, and provided a comprehensive assessment of restoration success with the goal of determining how the restoration process might be improved
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