1,997 research outputs found
Leveraging immigrant remittances for development
Some observers have suggested that one way to draw immigrants into the financial system is for banks to tap the large global remittance market. The authors of this article propose a model that would leverage remittances to both draw immigrants into the banking system as well promote economic development in immigrant communities in the United States and immigrants’ home countries.Emigrant remittances
Self-consistent Fermi surface renormalization of two coupled Luttinger liquids
Using functional renormalization group methods, we present a self-consistent
calculation of the true Fermi momenta k_F^a (antibonding band) and k_F^b
(bonding band) of two spinless interacting metallic chains coupled by small
interchain hopping. In the regime where the system is a Luttinger liquid, we
find that Delta = k_F^b - k_F^a is self-consistently determined by Delta =
Delta_{1} [ 1 + {g}_0^2 ln (Lambda_0 / Delta)^2]^{-1} where g_0 is the
dimensionless interchain backscattering interaction, Delta_{1} is the
Hartree-Fock result for k_F^{b}-k_F^a, and Lambda_0 is an ultraviolet cutoff.
If {g}_0^2 ln (Lambda_0 / Delta_{1})^2 is much larger than unity than even weak
interachain backscattering leads to a strong reduction of the distance between
the Fermi momenta.Comment: extended version with additional technical details; 5 RevTex pages, 2
figures; to appear in Phys. Rev.
Blazes: Coordination Analysis for Distributed Programs
Distributed consistency is perhaps the most discussed topic in distributed
systems today. Coordination protocols can ensure consistency, but in practice
they cause undesirable performance unless used judiciously. Scalable
distributed architectures avoid coordination whenever possible, but
under-coordinated systems can exhibit behavioral anomalies under fault, which
are often extremely difficult to debug. This raises significant challenges for
distributed system architects and developers. In this paper we present Blazes,
a cross-platform program analysis framework that (a) identifies program
locations that require coordination to ensure consistent executions, and (b)
automatically synthesizes application-specific coordination code that can
significantly outperform general-purpose techniques. We present two case
studies, one using annotated programs in the Twitter Storm system, and another
using the Bloom declarative language.Comment: Updated to include additional materials from the original technical
report: derivation rules, output stream label
Toward Domain-Specific Solvers for Distributed Consistency
To guard against machine failures, modern internet services store multiple replicas of the same application data within and across data centers, which introduces the problem of keeping geo-distributed replicas consistent with one another in the face of network partitions and unpredictable message latency. To avoid costly and conservative synchronization protocols, many real-world systems provide only weak consistency guarantees (e.g., eventual, causal, or PRAM consistency), which permit certain kinds of disagreement among replicas.
There has been much recent interest in language support for specifying and verifying such consistency properties. Although these properties are usually beyond the scope of what traditional type checkers or compiler analyses can guarantee, solver-aided languages are up to the task. Inspired by systems like Liquid Haskell [Vazou et al., 2014] and Rosette [Torlak and Bodik, 2014], we believe that close integration between a language and a solver is the right path to consistent-by-construction distributed applications. Unfortunately, verifying distributed consistency properties requires reasoning about transitive relations (e.g., causality or happens-before), partial orders (e.g., the lattice of replica states under a convergent merge operation), and properties relevant to message processing or API invocation (e.g., commutativity and idempotence) that cannot be easily or efficiently carried out by general-purpose SMT solvers that lack native support for this kind of reasoning.
We argue that domain-specific SMT-based tools that exploit the mathematical foundations of distributed consistency would enable both more efficient verification and improved ease of use for domain experts. The principle of exploiting domain knowledge for efficiency and expressivity that has borne fruit elsewhere - such as in the development of high-performance domain-specific languages that trade off generality to gain both performance and productivity - also applies here. Languages augmented with domain-specific, consistency-aware solvers would support the rapid implementation of formally verified programming abstractions that guarantee distributed consistency. In the long run, we aim to democratize the development of such domain-specific solvers by creating a framework for domain-specific solver development that brings new theory solver implementation within the reach of programmers who are not necessarily SMT solver internals experts
On tidal forces in f(R) theories of gravity
Despite the extraordinary attention that modified gravity theories have
attracted over the past decade, the geodesic deviation equation in this context
has not received proper formulation thus far. This equation provides an elegant
way to investigate the timelike, null and spacelike structure of spacetime
geometries. In this investigation we provide the full derivation of this
equation in situations where General Relativity has been extended in
Robertson-Walker background spacetimes. We find that for null geodesics the
contribution arising from the geometrical new terms is in general non-zero.
Finally we apply the results to a well known class of f(R) theories, compare
the results with General Relativity predictions and obtain the equivalent area
distance relation.Comment: 9 pages, 2 figure
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