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991.
A nonparametric version of the Final Prediction Error (FPE) is analysed for lag selection in nonlinear autoregressive time series under very general conditions including heteroskedasticity. We prove consistency and derive probabilities of incorrect selections that have been previously unavailable. Since it is more likely to overfit (have too many lags) than to underfit (miss some lags), a correction factor is proposed to reduce overfitting and hence increase correct fitting. For the FPE calculation, the local linear estimator is introduced in addition to the Nadaraya-Watson estimator in order to cover a very broad class of processes. To achieve faster computation, a plug-in band-width is suggested for the local linear estimator. Our Monte-Carlo study corroborates that the correction factor generally improves the probability of correct lag selection for both linear and nonlinear processes and that the plug-in bandwidth works at least as well as its commonly used competitor. The proposed methods are applied to the Canadian lynx data and daily returns of DM/US-Dollar exchange rates. 相似文献
992.
A central question in computational biology is the design of genetic
markers to distinguish between two given sets of (DNA) sequences. This question is formalized as
the NP-complete Distinguishing Substring Selection problem (DSSS for short) which asks, given a set of "good" strings and
a set of "bad" strings, for a solution string which is, with respect to the Hamming metric, "away" from the good strings and
"close" to the bad strings. More precisely, given integers dg, db, and L, we ask for a length-L string s such that s has Hamming distance at least dg to every length-L substring of the good strings and such that every bad string has a length-L substring with Hamming distance
at most db to s. Studying the parameterized complexity of DSSS, we show that, already for binary alphabet, DSSS is W[1]-hard with respect
to its natural parameters. This, in particular, implies that a recently given polynomial-time approximation scheme (PTAS)
by Deng et al. cannot be replaced by a so-called efficient polynomial-time approximation scheme (EPTAS) unless an unlikely
collapse in parameterized complexity theory occurs. This is seemingly the first computational biology problem for which such
a border between PTAS (which exists) and EPTAS (which is unlikely to exist) could be established. By way of contrast, for
a special case of DSSS, we present an exact fixed-parameter algorithm solving the problem efficiently. In this way we also
exhibit a sharp border between fixed-parameter tractability and intractability results. 相似文献
993.
994.
Dr. Julia Kriegesmann Dr. Thomas Schlatzer Dr. Kateryna Che Claudia Altdorf Dr. Susanne Huhmann Dr. Hanspeter Kählig Prof. Dr. Dennis Kurzbach Prof. Dr. Rolf Breinbauer Prof. Dr. Christian F. W. Becker 《Chembiochem : a European journal of chemical biology》2023,24(13):e202300098
Over the past decades, several strategies for inducing and stabilizing secondary structure formation in peptides have been developed to increase their proteolytic stability and their binding affinity to specific interaction partners. Here, we report how our recently introduced chemoselective Pd-catalyzed cysteine allylation reaction can be extended to stapling and how the resulting alkene-containing staples themselves can be further modified to introduce additional probes into such stabilized peptides. The latter is demonstrated by introducing a fluorophore as well as a PEG moiety into different stapled peptides using bioorthogonal thiol-ene and Diels-Alder reactions. Furthermore, we investigated structural implications of our allyl staples when used to replace conformationally relevant disulfide bridges. To this end, we chose a selective binder of integrin α3β1 (LXY3), which is only active in its cyclic disulfide form. We replaced the disulfide bridge by different stapling reagents in order to increase stability and binding affinity towards integrin α3β1. 相似文献
995.
Henrik C. M. Andersson Rolf Sandstrm 《International Journal of Pressure Vessels and Piping》2001,78(11-12)
Creep crack growth (CCG) has been studied for ex-service weld metal of 2.25Cr1Mo (P22). The testing was conducted at a temperature of 550°C and prior to testing, the material had been exposed to high temperature service for 110 000 h at 530°C. The results show a marked effect of the service exposure on the CCG properties of the material when compared to similar testing performed on a new material. The CCG rate was higher by a factor 3.1 in the service-exposed material, which should be compared to the model value of 3.2 based on the relations between the elongation values. The consumed deformation capacity was also estimated with the omega model for tertiary creep. In this case, an enhanced growth rate of 2.4 was obtained. Within a distance of about 10 mm in front of the propagating cracks, the number of creep cavities was significantly higher than in the surrounding material. The variation of the density of cavities as a function of distance from the crack tip was successfully modelled. 相似文献
996.
Rolf Berghammer Weiping Hu Arman Hasani Günter Gottstein 《Advanced Engineering Materials》2011,13(4):232-236
Ultrafine grained material was produced by equal channel angular pressing and confined channel die pressing. Microstructure and mechanical properties of the obtained samples were compared. The different effects on microstructure evolution and mechanical properties from both processes are discussed. 相似文献
997.
Michael R. Fellows Jiong Guo Hannes Moser Rolf Niedermeier 《Journal of Computer and System Sciences》2011,77(6):1141-1158
The Nemhauser–Trotter local optimization theorem applies to the NP-hard Vertex Cover problem and has applications in approximation as well as parameterized algorithmics. We generalize Nemhauser and Trotter?s result to vertex deletion problems, introducing a novel algorithmic strategy based on purely combinatorial arguments (not referring to linear programming as the Nemhauser–Trotter result originally did). The essence of our strategy can be understood as a doubly iterative process of cutting away “easy parts” of the input instance, finally leaving a “hard core” whose size is (almost) linearly related to the cardinality of the solution set. We exhibit our approach using a generalization of Vertex Cover, called Bounded-Degree Vertex Deletion. For some fixed d?0, Bounded-Degree Vertex Deletion asks to delete at most k vertices from a graph in order to transform it into a graph with maximum vertex degree at most d. Vertex Cover is the special case of d=0. Our generalization of the Nemhauser–Trotter-Theorem implies that Bounded-Degree Vertex Deletion, parameterized by k, admits an O(k)-vertex problem kernel for d?1 and, for any ?>0, an O(k1+?)-vertex problem kernel for d?2. Finally, we provide a W[2]-completeness result for Bounded-Degree Vertex Deletion in case of unbounded d-values. 相似文献
998.
Merit indices are used to rank materials and are of fundamental importance in materials selection. Traditionally, merit indices have only been available for elementary design cases. In the present paper merit indices are generalised to cooling systems where heat flow and strength are design criteria in a materials optimisation framework. A cooling tube and a cooling plate are considered. A new concept, merit exponent is used that is related to the merit indices. A definition of the merit exponent is given also for cases with many design variables. In each design case a number of merit exponents are involved. It is a nontrivial task to identify which they are and when each of them is applicable. For this purpose control area diagrams (CAD) are used. A CAD is a diagram with the controlling properties on the axes, and areas where one or more constraints are active. For the cooling systems the controlling properties are heat conductivity and strength. The active constraints define the relevant merit exponent. The constraints involve the controlling properties and geometrical variables. Principles are established for how to set up the CAD and to derive the merit exponents. 相似文献
999.
CO2 removal from exhaust gasses from burning of fossil fuels is a political issue. If undertaken on a large scale, enormous amounts of carbon dioxide will have to be taken care of. This paper investigates how mechanical activation of olivine and other Ca or Mg containing silicates can increase the mineral’s reactivity. Tests by grinding in a planetary mill have been done to investigate the effects of mechanical activation and other surface changes. The reactivity towards HCl and CO2 has been determined as a function of grinding variables. Prolonged dry milling of olivine resulted in highly aggregated products, which were more reactive with respect to dissolution in acid than their respective BET surface areas would suggest. The initial breaking of bonds appears to give more reactivity on an energy usage basis than longer time activation. Most mechanical activation testwork so far has been carried out in batch mode. The result is diminishing effect of activation with increased grinding time. Continuous grinding and simultaneous reaction with some sort of classification may offer a chance of removing reaction products as soon as they are formed, giving a more energy effective process. 相似文献
1000.
Schr?ter Hannes; Fiedler Anja; Miller Jeff; Ulrich Rolf 《Canadian Metallurgical Quarterly》2011,37(5):1361
In a simple reaction time (RT) experiment, visual stimuli were stereoscopically presented either to one eye (single stimulation) or to both eyes (redundant stimulation), with brightness matched for single and redundant stimulations. Redundant stimulation resulted in two separate percepts when noncorresponding retinal areas were stimulated, whereas it resulted in a single fused percept when corresponding areas were stimulated. With stimulation of noncorresponding areas, mean RT was shorter to redundant than to single stimulation, replicating the redundant signals effect (RSE) commonly found with visual stimuli. With stimulation of corresponding areas, however, no RSE was observed. This suggests that the RSE is driven by the number of percepts rather than by the number of stimulated receptors or sensory organs. These results are consistent with previous findings in the auditory modality and have implications for models of the RSE. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献