排序方式: 共有40条查询结果,搜索用时 15 毫秒
11.
Efstathios Bakolas Panagiotis Tsiotras 《Journal of Optimization Theory and Applications》2011,150(2):233-250
We consider a variation of the classical Markov–Dubins problem dealing with curvature-constrained, shortest paths in the plane with prescribed initial and terminal positions and tangents, when the lower and upper bounds of the curvature of the path are not necessarily equal. The motivation for this problem stems from vehicle navigation applications, when a vehicle may be biased in taking turns at a particular direction due to hardware failures or environmental conditions. After formulating the shortest path problem as a minimum-time problem, a family of extremals, which is sufficient for optimality, is characterized, and subsequently the complete analytic solution of the optimal synthesis problem is presented. In addition, the synthesis problem, when the terminal tangent is free, is also considered, leading to the characterization of the set of points that can be reached in the plane by curves satisfying asymmetric curvature constraints. 相似文献
12.
Dimitrios E. PanayotounakosIoanna Rizou Efstathios E. Theotokoglou 《Applied mathematics and computation》2011,217(21):8534-8542
It is shown that the three nonlinear dynamic Euler ordinary differential equations (ODEs), concerning the motion of a rigid body free to rotate about a fixed point, are reduced, by means of a subsidiary function which is to be determined, to three Abel equations of the second kind of the normal form. Based on a recently developed mathematical construction concerning exact analytic solutions of the Abel nonlinear ODEs of the second kind, we perform a new mathematical solution for the classical dynamic Euler nonlinear ODEs. 相似文献
13.
Spyridon K. Charisis Irene I. Naoumidi Harilaos S. Ginis Efstathios T. Detorakis Miltiadis K. Tsilimbaris 《Photochemistry and photobiology》2010,86(1):194-199
We studied the effect on the intraocular pressure (IOP) and the ciliary body (CB) morphology after four consecutive contact transcleral photodynamic treatments of the ciliary body (CB-PDT) with verteporfin in pigmented rabbits. Twenty-two pigmented rabbits underwent CB-PDT (study group), performed once (six rabbits) or repeated for up to four times (16 rabbits). Six additional rabbits received only laser treatment without photosensitizer administration (control group). CB-PDT was performed in one eye in rabbits of the study group, with the fellow eye serving as internal control. Verteporfin dosage was 1 mg kg −1 as bolus injection and laser settings were 40 mW (600 μm core optical fiber) for 1.5 min per spot, for 10 spots. In repeated CB-PDT, treatments were performed in 4-day intervals. Daily IOP measurements were recorded. Histological studies were performed at selected time points. An IOP reduction, more sustained following repeated treatments, was detected in all treated eyes but not in fellow eyes or in the control group. On the average, the IOP was restored to pretreatment levels 4 days after the last treatment. No serious adverse events were observed and the CB architecture was intact at the end of the experiment. Repeated CB-PDT is safe and results in a short-term reduction of IOP. Induced CB alterations are reversible. 相似文献
14.
For time series that are not stationary, the block bootstrap method is not directly applicable. However, if the underlying stochastic structure is slowly changing with time, one may employ a local block-resampling procedure. We define such a procedure, and give an example of its applicability. To cite this article: E. Paparoditis, D.N. Politis, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 959–962. 相似文献
15.
Efstathios Bakolas 《Journal of Optimization Theory and Applications》2014,162(3):954-974
We address the minimum-time guidance problem for the so-called isotropic rocket in the presence of wind under an explicit constraint on the acceleration norm. We consider the guidance problem to a prescribed terminal position and a circular target set with a free terminal velocity in both cases. We employ standard techniques from optimal control theory to characterize the structure of the optimal guidance law as well as the corresponding minimum time-to-go function. It turns out that the complete characterization of the solution to the optimal control problem reduces to the solution of a system of nonlinear equations in triangular form. Numerical simulations, that illustrate the theoretical developments, are presented. 相似文献
16.
Efstathios Paparoditis Dimitris N. Politis 《Annals of the Institute of Statistical Mathematics》2000,52(1):139-159
We consider the problem of estimating the distribution of a nonparametric (kernel) estimator of the conditional expectation g(x; ) = E((X
t+1) | Y
t,m
= x) of a strictly stationary stochastic process {X
t
, t 1}. In this notation (·) is a real-valued Borel function and Y
t,m
a segment of lagged values, i.e., Yt,m=(Xt-i
1,Xt-i
2,...,Xt-i
m), where the integers i
i
, satisfy 0 i12...m>. We show that under a fairly weak set of conditions on {X
t
, t 1}, an appropriately designed and simple bootstrap procedure that correctly imitates the conditional distribution of X
t+1 given the selective past Y
t,m
, approximates correctly the distribution of the class of nonparametric estimators considered. The procedure proposed is entirely nonparametric, its main dependence assumption refers to a strongly mixing process with a polynomial decrease of the mixing rate and it is not based on any particular assumptions on the model structure generating the observations. 相似文献
17.
Giorgos Athanasellis Efstathios Gavrielatos Olga Igglessi‐Markopoulou 《Journal of heterocyclic chemistry》2001,38(5):1203-1208
A new series of 5‐arylidene‐3‐substituted tetramic acids 6–19 have been synthesized by a condensation reaction of 3‐butanoyl tetramic acid 3 , 3‐ethoxycarbonyl tetramic acid 4 and 3 ‐acetyl tetramic acid 5 with a variety of substituted benzaldehydes. The structures of the isolated compounds 6–19 have been elucidated using FT‐IR, 1H and 13C‐NMR spectroscopy, FAB‐MS spectroscopy as well as elemental analyses. 相似文献
18.
19.
Athanassios C. Tsipis Ioannis G. Depastas Efstathios E. Karagiannis Constantinos A. Tsipis 《Journal of computational chemistry》2010,31(2):431-446
Magnetoresponsive three‐membered rings of d‐ and f‐block elements have been thoroughly investigated with the help of electronic structure calculation methods. The magnetic response of the clusters was evaluated by the Nucleus Independent Chemical Shifts (NICS)zz‐scan curves, which in conjunction with symmetry‐based selection rules for the most significant translationally and rotationally allowed transitions helped rationalize and predict the orbital‐type of aromaticity/antiaromaticity of the clusters. The magnetoresponsive early (Groups 3, 4, and 5) transition metal M3 rings exhibit successive aromatic and antiaromatic zones separated by a nodal plane. The magnetoresponsive late (Groups 11 and 12) transition metal M3 rings exhibit long‐range aromatic zone with the NICSzz(R) values decaying rapidly and monotonically with respect to R. The magnetic response of Group 10 transition metal M3 rings is similar to that of the early transition metal M3 rings, but it is long‐range antiaromatic only for the [c‐Ni3] cluster. The NICSzz‐scan curve of the [(HtLa)3(μ2‐H)6] cluster is indicative of weak pure σ‐aromaticity due to the induced diatropic ring current from the translationally allowed a → e′ and e′ → a transitions. The aromatic–antiaromatic behavior of the [(HtCe)3(μ2‐H)6]+ and [(HtTm)3(μ2‐H)6]2− clusters is similar to that of the early d‐block elements. The magnetic response of [(HtYb)3(μ2‐H)6]3− is similar to that of [c‐Hg3]2−. The [(HtLu)3(μ2‐H)6] cluster can be considered as a doubly (σ + π) aromatic system, with the σ‐aromatic component being much stronger than the π‐aromatic one. Finally, the [(XtRe)3(μ2‐X)6] and [(XtRu)3(μ2‐X)6]+ (X = Cl, Br, I) clusters exhibit significant aromatic character with the greatest contribution to the induced diatropic ring currents coming from π‐type transitions. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010 相似文献
20.
Efstathios Gavrielatos Giorgos Athanasellis Olga Igglessi‐Markopoulou 《Journal of heterocyclic chemistry》2002,39(1):185-188
The synthesis of a series of optically active N‐acetyl butenoates 3–5 is described using a facile methodology. These butenoates undergo cyclization to the corresponding N‐acetyl‐2‐alkyl‐pyrrolin‐4‐ones 6,7 retaining their stereochemical integrity. The structure of the newly synthesized compounds has been elucidated through 1H‐13C NMR, IR spectroscopy and their enantiomeric excesses have been measured by chiral HPLC analysis. 相似文献