1,280 research outputs found
Compact operators
All compact operators have a representation analogous to that
for compact normal operators. As a partial converse we obtain conditions which
allow one to construct a large number of such operators. Using the results in
the paper, we answer a number of questions about the decomposition of a compact
into real and imaginary parts
Securing The Root: A Proposal For Distributing Signing Authority
Management of the Domain Name System (DNS) root zone file is a uniquely global policy problem. For the Internet to connect everyone, the root must be coordinated and compatible. While authority over the legacy root zone file has been contentious and divisive at times, everyone agrees that the Internet should be made more secure. A newly standardized protocol, DNS Security Extensions (DNSSEC), would make the Internet's infrastructure more secure. In order to fully implement DNSSEC, the procedures for managing the DNS root must be revised. Therein lies an opportunity. In revising the root zone management procedures, we can develop a new solution that diminishes the impact of the legacy monopoly held by the U.S. government and avoids another contentious debate over unilateral U.S. control. In this paper we describe the outlines of a new system for the management of a DNSSEC-enabled root. Our proposal distributes authority over securing the root, unlike another recently suggested method, while avoiding the risks and pitfalls of an intergovernmental power sharing scheme
Regional Address Registries, Governance and Internet Freedom
Regional Internet Address Registries (RIRs) are private, nonprofit and transnational governance entities that evolved organically with the growth of the Internet to manage and coordinate Internet Protocol addresses. The RIR's management of Internet address resources is becoming more contentious and more central to global debates over Internet governance. This is happening because of two transformational problems: 1) the depletion of the IPv4 address space; and 2) the attempt to introduce more security into the Internet routing system. We call these problems "transformational" because they raise the stakes of the RIR's policy decisions, make RIR processes more formal and institutionalized, and have the potential to create new, more centralized control mechanisms over Internet service providers and users. A danger in this transition is that the higher stakes and centralized control mechanisms become magnets for political contention, just as ICANN's control of the DNS root did. In order to avoid a repeat of the problems of ICANN, we need to think carefully about the relationship between RIRs, governments, and Internet freedom. In particular, we need to shield RIRs from interference by national governments, and strengthen and institutionalize their status as neutral technical coordinators with limited influence over other areas of Internet governance
Investigating Simple Object Representations in Model-Free Deep Reinforcement Learning
We explore the benefits of augmenting state-of-the-art model-free deep
reinforcement algorithms with simple object representations. Following the
Frostbite challenge posited by Lake et al. (2017), we identify object
representations as a critical cognitive capacity lacking from current
reinforcement learning agents. We discover that providing the Rainbow model
(Hessel et al.,2018) with simple, feature-engineered object representations
substantially boosts its performance on the Frostbite game from Atari 2600. We
then analyze the relative contributions of the representations of different
types of objects, identify environment states where these representations are
most impactful, and examine how these representations aid in generalizing to
novel situations
Reinventing Media Activism: Public Interest Advocacy in the Making of U.S. Communication-Information Policy, 1960-2002
This report is a long-term analysis of citizens' collective action to influence public policy toward communication and information. The work discusses in greater detail what is meant by communication and information policy (CIP) and why we think it is worthwhile to study it as a distinctive domain of public policy and citizen action. The report concentrates on citizen action in the United States and looks backwards, tracing the long-term evolutionary trajectory of communications-information advocacy in the USA since the 1960s. We focus on the concept of citizen collective action and explain its relevance to CIP.Research supported by the Ford Foundation's Knowledge, Creativity and Freedom Program. The views expressed are those of the author and do not necessarily represent the views of the School of Information Studies, Syracuse University, or the Ford Foundation
Implementation of rigorous renormalization group method for ground space and low-energy states of local Hamiltonians
The practical success of polynomial-time tensor network methods for computing
ground states of certain quantum local Hamiltonians has recently been given a
sound theoretical basis by Arad, Landau, Vazirani, and Vidick. The convergence
proof, however, relies on "rigorous renormalization group" (RRG) techniques
which differ fundamentally from existing algorithms. We introduce an efficient
implementation of the theoretical RRG procedure which finds MPS ansatz
approximations to the ground spaces and low-lying excited spectra of local
Hamiltonians in situations of practical interest. In contrast to other schemes,
RRG does not utilize variational methods on tensor networks. Rather, it
operates on subsets of the system Hilbert space by constructing approximations
to the global ground space in a tree-like manner. We evaluate the algorithm
numerically, finding similar performance to DMRG in the case of a gapped
nondegenerate Hamiltonian. Even in challenging situations of criticality, or
large ground-state degeneracy, or long-range entanglement, RRG remains able to
identify candidate states having large overlap with ground and low-energy
eigenstates, outperforming DMRG in some cases.Comment: 13 pages, 10 figure
Deconfined quantum critical point in one dimension
We perform a numerical study of a spin-1/2 model with symmetry in one dimension which demonstrates an interesting
similarity to the physics of two-dimensional deconfined quantum critical points
(DQCP). Specifically, we investigate the quantum phase transition between Ising
ferromagnetic and valence bond solid (VBS) symmetry-breaking phases. Working
directly in the thermodynamic limit using uniform matrix product states, we
find evidence for a direct continuous phase transition that lies outside of the
Landau-Ginzburg-Wilson paradigm. In our model, the continuous transition is
found everywhere on the phase boundary. We find that the magnetic and VBS
correlations show very close power law exponents, which is expected from the
self-duality of the parton description of this DQCP. Critical exponents vary
continuously along the phase boundary in a manner consistent with the
predictions of the field theory for this transition. We also find a regime
where the phase boundary splits, as suggested by the theory, introducing an
intermediate phase of coexisting ferromagnetic and VBS order parameters.
Interestingly, we discover a transition involving this coexistence phase which
is similar to the DQCP, being also disallowed by Landau-Ginzburg-Wilson
symmetry-breaking theory.Comment: 20 pages, 18 figure
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