2,173 research outputs found
Energy-Efficient Algorithms
We initiate the systematic study of the energy complexity of algorithms (in
addition to time and space complexity) based on Landauer's Principle in
physics, which gives a lower bound on the amount of energy a system must
dissipate if it destroys information. We propose energy-aware variations of
three standard models of computation: circuit RAM, word RAM, and
transdichotomous RAM. On top of these models, we build familiar high-level
primitives such as control logic, memory allocation, and garbage collection
with zero energy complexity and only constant-factor overheads in space and
time complexity, enabling simple expression of energy-efficient algorithms. We
analyze several classic algorithms in our models and develop low-energy
variations: comparison sort, insertion sort, counting sort, breadth-first
search, Bellman-Ford, Floyd-Warshall, matrix all-pairs shortest paths, AVL
trees, binary heaps, and dynamic arrays. We explore the time/space/energy
trade-off and develop several general techniques for analyzing algorithms and
reducing their energy complexity. These results lay a theoretical foundation
for a new field of semi-reversible computing and provide a new framework for
the investigation of algorithms.Comment: 40 pages, 8 pdf figures, full version of work published in ITCS 201
Ward Identities and chiral anomalies for coupled fermionic chains
Coupled fermionic chains are usually described by an effective model written
in terms of bonding and anti-bonding spinless fields with linear dispersion in
the vicinities of the respective Fermi points. We derive for the first time
exact Ward Identities (WI) for this model, proving the existence of chiral
anomalies which verify the Adler-Bardeen non-renormalization property. Such WI
are expected to play a crucial role in the understanding of the thermodynamic
properties of the system. Our results are non-perturbative and are obtained
analyzing Grassmann functional integrals by means of Constructive Quantum Field
Theory methods.Comment: TeX file, 26 pages, 7 figures. Published version, new section added
to answer referee remarks and derive the Ward Identites, no modifications in
the main resul
Determinants of fibrinogen in an Italian population suffering from claudication. Lower fibrinogen in the south compared to middle and north of Italy. The ADEP Group.
Prospective studies have shown that high plasma levels of fibrinogen are independently associated with the risk of cardiovascular complications. In patients suffering from peripheral vascular disease (PVD) fibrinogen has been shown to be an independent predictor of cardiovascular disease but its determinants have never been examined in this clinical setting. DESIGN AND METHODS: Fibrinogen levels were related to clinical and laboratory variables in 2,111 patients suffering from PVD. We also analyzed whether there was a regional distribution of risk factors. RESULTS: The median values of fibrinogen was 312 mg/dL. The clinical variables examined did not differentiate patients with elevated or normal fibrinogen levels. In particular, patients with ankle/arm pressure ratio < 0.8 did not show a higher prevalence of fibrinogen > 312 mg/dL. Conversely, white blood cell (WBC) count and serum cholesterol levels were significantly associated with high fibrinogen levels (p < 0.0001). Multiple logistic regression analysis demonstrated that areas of Italy were differently associated with high plasma fibrinogen levels (p < 0.03): subjects in the north and middle of Italy having significantly higher values of fibrinogen than subjects in the south of Italy (p < 0.01). A similar regional distribution was observed for WBC count and serum cholesterol levels. INTERPRETATION AND CONCLUSIONS: The regional distribution of risk factors raises the question as to whether the already reported large variability of cardiovascular events so in PVD may be attributed to a non homogeneous distribution of risk factors
Conductivity between Luttinger liquids: coupled chains and bilayer graphene
The conductivity properties between Luttinger liquids are analyzed by exact
Renormalization Group methods. We prove that in a two chain system or in a
model of bilayer graphene, described by two coupled fermionic honeycomb
lattices interacting with a gauge field, the transverse optical conductivity at
finite temperature is anomalous and decreasing together with the frequency as a
power law with Luttinger liquid exponent.Comment: Title changed, new section on bilayer graphene adde
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