448 research outputs found
Efficient rewriting techniques
This thesis considers three aspects of the (efficient) implementation of term rewrite systems. For efficient matching of terms against rules we introduce a formal notion of match trees. These match trees can be used to simultaneously match a term against multiple rewrite rules. The second aspect is that of temporary-term construction. After each application of a rewrite rule, a new (often temporary) term is constructed. In order to make rewriting as efficient as possible, it is shown how to annotate these temporary terms such that the information about which (sub)terms are already rewritten to normal form is preserved. This allows strategies to be written such that these subterms, known to be in normal form, will not be considered a second time. To avoid needless construction of temporary terms, it is also shown how to determine what subterms will be rewritten later on for sure, allowing for immediate rewriting of such terms. Finally, the notion of strategy trees is introduced. These strategy trees allow for a flexible specification of lazy rewrite strategies. Conditions are given for strategy trees that guarantee that rewriting a term results in a normal form of that term. Also, a method is given to automatically generate strategy trees that satisfy these conditions
First constraint on cosmological variation of the proton-to-electron mass ratio from two independent telescopes
A high signal-to-noise spectrum covering the largest number of hydrogen lines
(90 H2 lines and 6 HD lines) in a high redshift object was analyzed from an
observation along the sight-line to the bright quasar source J2123005 with
the UVES spectrograph on the ESO Very Large Telescope (Paranal, Chile). This
delivers a constraint on a possible variation of the proton-to-electron mass
ratio of Dmu/mu = (8.5 \pm 3.6_{stat} \pm 2.2_{syst}) x 10^{-6} at redshift
z=2.059$, which agrees well with a recently published result on the same system
observed at the Keck telescope yielding Dmu/mu = (5.6 \pm 5.5_{stat} \pm
2.9_{syst}) x 10^{-6}. Both analyses used the same robust absorption line
fitting procedures with detailed consideration of systematic errors.Comment: Accepte
An orbitally derived single-atom magnetic memory
A single magnetic atom on a surface epitomizes the scaling limit for magnetic
information storage. Indeed, recent work has shown that individual atomic spins
can exhibit magnetic remanence and be read out with spin-based methods,
demonstrating the fundamental requirements for magnetic memory. However, atomic
spin memory has been only realized on thin insulating surfaces to date,
removing potential tunability via electronic gating or distance-dependent
exchange-driven magnetic coupling. Here, we show a novel mechanism for
single-atom magnetic information storage based on bistability in the orbital
population, or so-called valency, of an individual Co atom on semiconducting
black phosphorus (BP). Distance-dependent screening from the BP surface
stabilizes the two distinct valencies and enables us to electronically
manipulate the relative orbital population, total magnetic moment and spatial
charge density of an individual magnetic atom without a spin-dependent readout
mechanism. Furthermore, we show that the strongly anisotropic wavefunction can
be used to locally tailor the switching dynamics between the two valencies.
This orbital memory derives stability from the energetic barrier to atomic
relaxation and demonstrates the potential for high-temperature single-atom
information storage
White Gaussian Noise Based Capacity Estimate and Characterization of Fiber-Optic Links
We use white Gaussian noise as a test signal for single-mode and multimode
transmission links and estimate the link capacity based on a calculation of
mutual information. We also extract the complex amplitude channel estimations
and mode-dependent loss with high accuracy.Comment: submitted to The Optical Networking and Communication Conference
(OFC) 201
112 Gbit/s single-polarization silicon coherent receiver with hybrid-integrated BiCMOS linear TIA
We report the design, fabrication and verification of a single-polarization silicon coherent receiver with a low-power linear TIA array. Error-free operation assuming FEC is shown at bitrates of 112 Gbit/s (28 Gbaud 16-QAM) and 56 Gbit/s (28 Gbaud QPSK)
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