Observation of amplified phase-conjugate reflection and optical parametric oscillation by degenerate four-wave mixing in a transparent medium

We report on the observation of amplified reflection and optical parametric oscillation via degenerate four-wave mixing in a nonresonant medium. The process is mediated through the third-order nonlinear susceptibility in a transparent liquid medium, CS2. A collinear mixing geometry is utilized to obtain long interaction lengths and polarization discrimination is used to separate the pump and signal fields

Compensation for channel dispersion by nonlinear optical phase conjugation

It is proposed that the process of nonlinear optical phase conjugation can be utilized to compensate for channel dispersion and hence to correct for temporal pulse broadening. Specifically, a four-wave nonlinear interaction is shown to achieve pulse renarrowing. Spectral bandwidth constraints of the input pulse are presented for typical phase-conjugate interaction parameters

Spatial convolution and correlation of optical fields via degenerate four-wave mixing

A nonlinear optical technique is described that performs, essentially instantaneously, the functions of spatial correlation and convolution of spatially encoded waves. These real-time operations are accomplished by mixing spatially dependent optical fields in the Fourier-transform plane of a lens system. The use of a degenerate four-wave mixing scheme eliminates (in the Fresnel approximation) phase-matching restrictions and (optical) frequency-scaling factors. Spatial bandwidth-gain considerations and numerical examples, as well as applications to nonlinear microscopy, are presented

Image phase compensation and real-time holography by four-wave mixing in optical fibers

It is proposed that real-time holography can be performed inside multimode fibers (or optical waveguides) using four-wave optical mixing. Of particular interest is the generation of complex-conjugate replicas of input fields for image transmission and compensation of propagation distortion. A theoretical analysis and a numerical estimate are presented

A theoretical and experimental investigation of the modes of optical resonators with phase-conjugate mirrors

We present an analysis of resonator properties for a cavity bounded by a phase conjugate mirror, which is generated by a degenerate four-wave nonlinear optical interaction. Using a ray matrix formalism to describe the conjugate mirror, resonator stability conditions are derived. Longitudinal and transverse mode characteristics are discussed. Results are compared with an experiment where laser oscillation was observed at 6943 Å using carbon disulfide as the nonlinear interacting medium comprising the phase conjugate mirror

Learning to Crawl

Web crawling is the problem of keeping a cache of webpages fresh, i.e., having the most recent copy available when a page is requested. This problem is usually coupled with the natural restriction that the bandwidth available to the web crawler is limited. The corresponding optimization problem was solved optimally by Azar et al. [2018] under the assumption that, for each webpage, both the elapsed time between two changes and the elapsed time between two requests follow a Poisson distribution with known parameters. In this paper, we study the same control problem but under the assumption that the change rates are unknown a priori, and thus we need to estimate them in an online fashion using only partial observations (i.e., single-bit signals indicating whether the page has changed since the last refresh). As a point of departure, we characterise the conditions under which one can solve the problem with such partial observability. Next, we propose a practical estimator and compute confidence intervals for it in terms of the elapsed time between the observations. Finally, we show that the explore-and-commit algorithm achieves an $\mathcal{O}(\sqrt{T})$ regret with a carefully chosen exploration horizon. Our simulation study shows that our online policy scales well and achieves close to optimal performance for a wide range of the parameters.Comment: Published at AAAI 202

Q-switched ruby laser alloying of Ohmic contacts on gallium arsenide epilayers

Ohmic contacts of AuGe have been produced on GaAs epilayers by laser alloying. The contacts possess morphological and electrical properties which are superior to those formed by conventional alloying

Technology Selection for Big Data and Analytical Applications

The term Big Data has become pervasive in recent years, as smart phones, televisions, washing machines, refrigerators, smart meters, diverse sensors, eyeglasses, and even clothes connect to the Internet. However, their generated data is essentially worthless without appropriate data analytics that utilizes information retrieval, statistics, as well as various other techniques. As Big Data is commonly too big for a single person or institution to investigate, appropriate tools are being used that go way beyond a traditional data warehouse and that have been developed in recent years. Unfortunately, there is no single solution but a large variety of different tools, each of which with distinct functionalities, properties and characteristics. Especially small and medium-sized companies have a hard time to keep track, as this requires time, skills, money, and specific knowledge that, in combination, result in high entrance barriers for Big Data utilization. This paper aims to reduce these barriers by explaining and structuring different classes of technologies and the basic criteria for proper technology selection. It proposes a framework that guides especially small and mid-sized companies through a suitable selection process that can serve as a basis for further advances

The Geometric Maximum Traveling Salesman Problem

We consider the traveling salesman problem when the cities are points in R^d for some fixed d and distances are computed according to geometric distances, determined by some norm. We show that for any polyhedral norm, the problem of finding a tour of maximum length can be solved in polynomial time. If arithmetic operations are assumed to take unit time, our algorithms run in time O(n^{f-2} log n), where f is the number of facets of the polyhedron determining the polyhedral norm. Thus for example we have O(n^2 log n) algorithms for the cases of points in the plane under the Rectilinear and Sup norms. This is in contrast to the fact that finding a minimum length tour in each case is NP-hard. Our approach can be extended to the more general case of quasi-norms with not necessarily symmetric unit ball, where we get a complexity of O(n^{2f-2} log n). For the special case of two-dimensional metrics with f=4 (which includes the Rectilinear and Sup norms), we present a simple algorithm with O(n) running time. The algorithm does not use any indirect addressing, so its running time remains valid even in comparison based models in which sorting requires Omega(n \log n) time. The basic mechanism of the algorithm provides some intuition on why polyhedral norms allow fast algorithms. Complementing the results on simplicity for polyhedral norms, we prove that for the case of Euclidean distances in R^d for d>2, the Maximum TSP is NP-hard. This sheds new light on the well-studied difficulties of Euclidean distances.Comment: 24 pages, 6 figures; revised to appear in Journal of the ACM. (clarified some minor points, fixed typos

Design of parking solutions in the locality street Gen. Sochora and neighborhood

Předmětem diplomové práce je zhodnocení původního stavu statické dopravy řešeného území, následný výpočet potřebného počtu nových stání byl proveden pomocí normy ČSN 73 6110 a aktuální poptávky. Součástí diplomové práce je provedení dopravního průzkumu včetně analýzy bodových závad a dopravní nehodovosti. Dále byly navrženy dvě varianty řešení ke zkapacitnění parkovacích a odstavných stání včetně úprav ke zvýšení bezpečnosti a plynulosti provozu na místech kde byly zjištěny bodové závady. Prvním návrhem je varianta s parkovacím domem na ploše v blízkosti Sarezy a úpravou ulice náměstí Družby a Bajkalská na jednosměrný provoz, který zlepší bezpečnost a plynulost dopravy. Ve druhé variantě vznikne na ploše v blízkosti Sarezy parkovací plocha a okolní ulice budou navrženy pro větší kapacitu odstavných a parkovacích stání. Varianty byly navrženy s ohledem na návrhová vozidla a rozhledové poměry. Výsledná varianta obsahuje zhodnocení záborů pozemků, vzorové řezy, půdorys parkovacího domu, výkresy rozhledových poměrů a dopravního značení, ověření vlečných křivek vozidel a orientační odhad nákladů.The subject of this diploma thesis is the evaluation of the original state of static transport in the solved area, the subsequent calculation of the required number of parking spaces was done according to the norm ČSN 73 6110 and the current inquiry. Part of this diploma thesis is the execution of the traffic research including the analysis of conflict situations and the analysis of traffic accidents possibility. Furthermore, two variants of the solution for increasing the capacity of parking spaces were suggested including the adjustments for improvement of the safety and fluency of the traffic in the places where the conflict situations were detected. The first suggestion is the variant containing a parking house in the area nearby the Sareza covered pool and the adjustment of the náměstí Družby street and the Bajkalská street to one-way traffic which is going to improve the safety and fluency of the traffic in general. In the second proposal, parking area is going to be created in the area nearby the Sareza covered pool and the surrounding streets will be designed for bigger capacity of the parking spaces. The variants were created with regard to the design vehicle and lookout ratios. The resulting variant contains evaluation of the land annexation, modal sections, floor plan of the parking house, draft of lookout ratios and traffic signs, verification of the towing vehicles curves and tentative costs estimation.227 - Katedra dopravního stavitelstvívelmi dobř