3,483 research outputs found
Exact Synchronization for Finite-State Sources
We analyze how an observer synchronizes to the internal state of a
finite-state information source, using the epsilon-machine causal
representation. Here, we treat the case of exact synchronization, when it is
possible for the observer to synchronize completely after a finite number of
observations. The more difficult case of strictly asymptotic synchronization is
treated in a sequel. In both cases, we find that an observer, on average, will
synchronize to the source state exponentially fast and that, as a result, the
average accuracy in an observer's predictions of the source output approaches
its optimal level exponentially fast as well. Additionally, we show here how to
analytically calculate the synchronization rate for exact epsilon-machines and
provide an efficient polynomial-time algorithm to test epsilon-machines for
exactness.Comment: 9 pages, 6 figures; now includes analytical calculation of the
synchronization rate; updates and corrections adde
An inductively coupled plasma-time-of-flight mass spectrometer for elemental analysis. Part II: Direct current quadrupole lens system for improved performance
An electrostatic quadrupole lens has been substituted for a cylindrical lens system used in the original inductively coupled plasma-time-of-flight mass spectrometer (ICP-TOFMS). With an improved vacuum system also installed, the cylindrical and quadrupole lenses are compared to each other and to the performance of the prototype ICP-TOFMS. The quadrupole lens requires no tradeoff between ion throughput and resolving power as was encountered with cylindrical lenses. The background noise in both ion-optical systems is within the same order of magnitude. Images of the ion beam formed by each ion-optical system have been obtained on a microchannel plate-phosphor screen. The quadrupole lens shows a higher ion-beam flux and produces a slitlike focus required in the orthogonal ICP-TOFMS instrument. Signal-to-noise ratios in the ICP-TOFMS can be improved by using a technique called pulsed-ion injection that is particularly convenient with the quadrupole lens. In this technique, one quadrupole electrode is pulsed to prevent ions from entering the extraction zone except when an ion packet is to be extracted for mass analysis. This technique significantly reduces the noise over continuous ion injection. In the orthogonal ICP-TOFMS with pulsed-ion injection, 0.5 frnol of analyte could be detected in 1.4 ms with a proper data acquisition system. Overall, the combination of a quadrupole lens and pulsed-ion injection may provide detection limits for the ICP-TOFMS that are competitive with those of quadrupole inductively coupled plasma-mass spectrometry instruments
Five-year impact of repeated praziquantel treatment on subclinical morbidity due to Schistosoma japonicum in China
We report the 5-year impact (1996-2001) of repeated praziquantel chemotherapy on subclinical morbidity related to Schistosoma japonicum infection. We repeated stool examinations and hepatosplenic ultrasonography in a cohort of 120 individuals living on an island with endemic infection in Dongting Lake, China. Prevalence of schistosome infection fell by 43% and intensity (geometric mean eggs per gram) declined by 80% over the 5 years. However, transmission persisted at a dangerously high rate of 13% per year for re-infection or new infection in the cohort. The prevalence of left-lobe enlargement and dilated portal vein fell significantly (P 0.05). However, endpoint infection was even more strongly associated with left-lobe enlargement (57% versus 15%, P < 0.01). The proportions of subjects with improved parenchymal and periportal fibrosis were much higher than the proportions of subjects that progressed (P < 0.05). Reduction of prevalence and intensity of infection, and improvement of subclinical morbidity, were benefits of repeated treatments. Further research is needed to understand why some patients developed fibrosis despite substantial reductions in egg counts and to evaluate the functional importance of residual subclinical morbidity after chemotherapy-based control in the lake and marshland area of Chin
Two-year impact of praziquantel treatment for Schistosoma japonicum infection in China: re-infection, subclinical disease and fibrosis marker measurements
We studied a community cohort of 193 individuals exposed to endemic Schistosoma japonicum infection in the Dongting Lake region of China to assess subclinical morbidity and the 2-year benefit of curative therapy (praziquantel) administered in 1996. Prevalence and intensity of S. japonicum infection before treatment were 28% and 192 eggs per gram faeces (epg), respectively. Two years after cure, 22% of the cohort were reinfected, but with a lighter intensity (67 epg). Sixty-four subjects (37%) showed significant improvement in ultrasound parenchyma images after treatment and 51 subjects (54%) showed significant improvement of periportal fibrosis. Left-lobe enlargement also reversed (P 0·05). The serum levels of laminin and collagen IV associated with reinfection and intensity and hyaluronic acid levels correlated with ultrasound findings (P < 0·01). Overall, treatment induced a marked decrease in subclinical hepatosplenic morbidity attributable to S. japonicum although low-intensity re-infection after treatment remained relatively frequent. Stratified analysis and logistic models evaluated potential confounding factors for assessment of treatment effects on hepatic fibrosis. S. japonicum infection and moderate-heavy alcohol intake interacted: improvement in parenchymal morbidity was impeded among drinkers (P < 0·05). Chemotherapy focused on at-risk residents controls prevalent subclinical hepatic fibrosis but re-infection indicates the need for complementary control strategie
A novel robust disturbance rejection anti-windup framework
This is an Author's Original Manuscript of an article submitted for consideration in the International Journal of Control [copyright Taylor & Francis] and is available online at http://www.tandfonline.com/10.1080/00207179.2010.542774In this article, we propose a novel anti-windup (AW) framework for coping with input saturation in the disturbance rejection problem of stable plant systems. This framework is based on the one developed by Weston and Postlethwaite (W&P) (Weston, P.F., and Postlethwaite, I. (2000), ‘Linear Conditioning for Systems Containing Saturating Actuators’, Automatica, 36, 1347–1354). The new AW-design improves the disturbance rejection performance over the design framework usually suggested for the coprime-factorisation based W&P-approach. Performance improvement is achieved by explicitly incorporating a transfer function, which represents the effect of the disturbance on the nonlinear loop, into the AW compensator synthesis. An extra degree of freedom is exploited for the coprime factorisation, resulting in an implicitly computed multivariable algebraic loop for the AW-implementation. Suggestions are made to overcome the algebraic loop problem via explicit computation. Furthermore, paralleling the results of former work (Turner, M.C., Herrmann, G., and Postlethwaite, I. (2007), ‘Incorporating Robustness Requirements into Antiwindup Design’, IEEE Transactions on Automatic Control, 52, 1842–1855), the additive plant uncertainty is incorporated into the AW compensator synthesis, by using a novel augmentation for the disturbance rejection problem. In this new framework, it is shown that the internal model control (IMC) scheme is optimally robust, as was the case in Turner, Herrmann, and Postlethwaite (2007) and Zheng and Morari (Zheng, A., and Morari, M. (1994), ‘Anti-windup using Internal Model Control’, International Journal of Control, 60, 1015–1024). The new AW approach is applied to the control of dynamically substructured systems (DSS) subject to external excitation signals and actuator limits. The benefit of this approach is demonstrated in the simulations for a small-scale building mass damper DSS and a quasi-motorcycle DSS
Fractional Spin for Quantum Hall Effect Quasiparticles
We investigate the issue of whether quasiparticles in the fractional quantum
Hall effect possess a fractional intrinsic spin. The presence of such a spin
is suggested by the spin-statistics relation , with
being the statistical angle, and, on a sphere, is required for consistent
quantization of one or more quasiparticles. By performing Berry-phase
calculations for quasiparticles on a sphere we find that there are two terms,
of different origin, that couple to the curvature and can be interpreted as
parts of the quasiparticle spin. One, due to self-interaction, has the same
value for both the quasihole and quasielectron, and fulfills the
spin-statistics relation. The other is a kinematical effect and has opposite
signs for the quasihole and quasielectron. The total spin thus agrees with a
generalized spin-statistics theorem . On the
plane, we do not find any corresponding terms.Comment: 15 pages, RevTeX-3.
SU(4) Spin-Orbital Two-Leg Ladder, Square and Triangle Lattices
Based on the generalized valence bond picture, a Schwinger boson mean field
theory is applied to the symmetric SU(4) spin-orbital systems. For a two-leg
SU(4) ladder, the ground state is a spin-orbital liquid with a finite energy
gap, in good agreement with recent numerical calculations. In two-dimensional
square and triangle lattices, the SU(4) Schwinger bosons condense at
(\pi/2,\pi/2) and (\pi/3,\pi/3), respectively. Spin, orbital, and coupled
spin-orbital static susceptibilities become singular at the wave vectors, twice
of which the bose condensation arises at. It is also demonstrated that there
are spin, orbital, and coupled spin-orbital long-range orderings in the ground
state.Comment: 5 page
Quantitative determination of the local structure of thymine on Cu(1 1 0) using scanned-energy mode photoelectron diffraction
The local adsorption structures of the surface species formed by interaction of thymine with a Cu(1 1 0) surface at room temperature, and after heating to not, vert, similar530 K, have been investigated. Initial characterisation by soft-X-ray photoelectron spectroscopy and O K-edge near-edge X-ray absorption fine structure (NEXAFS) indicates the effect of sequential dehydrogenation of the NH species and provides information on the molecular orientation. O 1s and N 1s scanned-energy mode photoelectron diffraction shows the species at both temperatures bond to the surface through both carbonyl O atoms and the deprotonated N atom between them, each bonding atom adopting near-atop sites on the outermost Cu surface layer. The associated bondlengths are 1.96 ± 0.03 Å for Cu–N and 1.91 ± 0.03 Å and 2.03 ± 0.03 Å for the two inequivalent Cu--O bonds. The molecular plane lies almost exactly in the close-packed View the MathML source azimuth, but with a tilt relative to the surface normal of approximately 20°. Heating to not, vert, similar530 K, or deposition at this temperature, appears to lead to dehydrogenation of the second N atom in the ring, but no significant change in the adsorption geometry
Hopping Conduction in Disordered Carbon Nanotubes
We report electrical transport measurements on individual disordered carbon
nanotubes, grown catalytically in a nanoporous anodic aluminum oxide template.
In both as-grown and annealed types of nanotubes, the low-field conductance
shows as exp[-(T_{0}/T)^{1/2}] dependence on temperature T, suggesting that
hopping conduction is the dominant transport mechanism, albeit with different
disorder-related coefficients T_{0}. The field dependence of low-temperature
conductance behaves an exp[-(xi_{0}/xi)^{1/2}] with high electric field xi at
sufficiently low T. Finally, both annealed and unannealed nanotubes exhibit
weak positive magnetoresistance at low T = 1.7 K. Comparison with theory
indicates that our data are best explained by Coulomb-gap variable range
hopping conduction and permits the extraction of disorder-dependent
localization length and dielectric constant.Comment: 10 pages, 5 figure
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