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Molecular dynamics with Langevin equation using local harmonics and Chandrasekhar’s convolution
No full textA numerical method for studying molecular systems subject to a random force field leading to a Gaussian velocity distribution and described by the Langevin equation is presented. Two basic elements constitute the formulation: local harmonic modes and Chandrasekhar's formula for the distribution function for a convolution involving a random function. First, by linearizing the governing Langevin equations locally and employing an orthogonal change of coordinates, an explicit solution for the displacement and velocity is constructed. Second, Chandrasekhar's formula is employed in deriving the probability distribution function of the displacements and the velocities coming from the random forces. The local mode analysis is essential for the use of the Chandrasekhar's formula, since we need the formal solution as a convolution of the random forces and the local Green's function. For an illustration of the method in a significant case representative of real problems, we study a one dimensional idealization of a long chain molecule possessing internal energy barriers and subjected to an applied tension. The results are compared with the predictions of a conventional approximate method where a finite number of random realizations are generated in each time step. This truncation constitutes an approximation to obtain the desired Gaussian probability distribution function for the velocities which is reached in the limit of an infinity of random realizations. The calculations show that the conventional approximations may be acceptable only for short times, small temperatures, and average values over very long times. In particular, these approximations fail to give accurate results for transient phenomena, show slow convergence with the increase in the number of random realizations, and predict large values for the variance even in the steady regime. The new proposed method on the other hand, (i) incorporates the mathematically and conceptually correct limit for the distribution function, (ii) is quite stable with respect to increases in the value of the time increment as well as in terms of fluctuations characterized by the variance, (iii) leads to considerable savings in computer time over the approximate method, and (iv) has the proper description during the transient regime, which is usually the most interesting phase of dynamical processes
Preferential amplification of rising versus falling frequency whistler mode signals
No full textAnalysis of ground-based ELF/VLF observations of injected whistler mode waves from the 1986 Siple Station experiment demonstrates the preferential magnetospheric amplification of rising over descending frequency-time ramps. From examining conjugate region receptions of 1 kHz/s frequency-time ramps, we find that rising ramps generate an average total power 1.9 times higher than that of falling frequency ramps when both are observed during a transmission. And in 17% of receptions, only rising ramps are observed above the noise floor. Furthermore, the amplification ratio inversely correlates with the noise and total signal power. Using a narrowband Vlasov-Maxwell numerical simulation, we explore the preferential amplification due to differences in linear growth rate as a function of frequency, relative to the frequency which maximizes the linear growth rate for a given anisotropy, and in nonlinear phase trapping. These results contribute to the understanding of magnetospheric wave amplification and the preference for structured rising elements in chorus
Alpha-beta-conspiracy search
No full textWe introduce a variant of alpha-beta search in which each node is associated with two depths rather than one. The purpose of alpha-beta search is to find strategies for each player that together establish a value for the root position. A max strategy establishes a lower bound and the min strategy establishes an upper bound. It has long been observed that forced moves should be searched more deeply. Here we make the observation that in the max strategy we are only concerned with the forcedness of max moves and in the min strategy we are only concerned with the forcedness of min moves. This leads to two measures of depth - one for each strategy - and to a two-depth variant of alpha-beta called ABC search. The two-depth approach can be formally derived from conspiracy theory and the structure of the ABC procedure is justified by two theorems relating ABC search and conspiracy numbers
User interface paradigms for visually authoring mid-air gestures: a survey and a provocation
No full textGesture authoring tools enable the rapid and experiential prototyping of gesture-based interfaces. We survey visual authoring tools for mid-air gestures and identify three paradigms used for representing and manipulating gesture information: graphs, visual markup languages and timelines. We examine the strengths and limitations of these approaches and we propose a novel paradigm to authoring location-based mid-air gestures based on space discretization
A statistical subgrid scale model for large eddy simulations
No full textÇinlar velocity is a promising subgrid velocity model for large eddy simulation. The energy spectrum plays a central role for modeling the subgrid stress term in filtered Navier-Stokes equations. Considering a truncated Gamma distribution for radius of eddies, the subgrid scale energy spectrum has been computed analytically. In this study, we develop a new subgrid stress model for representing the small scale effects in LES by defining the parameters of the energy spectrum
Parylene based uncooled thermomechanical array
No full textNovel thermo-mechanical detector arrays with integrated diffraction grating for optical readout were designed and fabricated. Parylene was used as the structural material due to its high thermal isolation and mismatch properties. Calculations reveal that the NETD performance of a thermo-mechanical array using Parylene can be significantly better than SiNx based designs and offer a theoretical NETD value <10mK assuming an optical readout with a high dynamic range detector array. Finite Element simulations were performed with length of the bimaterial leg as the optimization parameter. It was observed that only a few microns of isolation leg supported 30 fps applications, leaving rest of the leg to be bimaterial and providing large thermo-mechanical deflections
Malatya - Relief B, Ankara 12252 [King (PUGNUS-mili) offering libation and an animal to the Storm God. Relief B]
No full textThis limestone relief is part of the Lion Gate. Block displaying offering scenes: On the right one the right king (PUGNUS-mili) is offering libation and an animal to the Storm God of the city (POCULUM-ta). They are dated to the 9th century BC, but arguments towards an earlier dating also exist. Currently housed by Anatolian Civilizations Museum in Ankara, No. 12252. Other reproduction of this image is GNT.S17.14.phg.01.Black & white photograph
Old sun disc as burial finding - Pre-Hittite Hattic religious standard, Alacahöyük
No full textImage of one of the burial findings, cult object found in the royal tombs of pre-Hittite (Hatti) times from 3rd millenium BC, represented to gods. It is currently housed in Anatolian Civilization Museum in Ankara.Black & white photograph
Lion Gate, Hattusa
No full textThe Lion Gate in the south-west of Hattusa. At Hattuša, the capital city of Hittites (today in the Çorum Province, Turkey) from their beginning in the 17th century BC until the collapse of the empire in early 12th century BC. By the 12th century the city came to cover an area of 182 hectars, surrounded by a 3.3 km long defensive wall. The Aslanlı Kapı (Lion Gate) with two stone lions were believed to protect the city from evil spirits. The Lion Gate was one of the six defensive walls of the city. Besides natural outcrops that were turned out to the part of the walls, massive ramparts were made to create artificial fortresses.Black & white photograph
Basalt slab with neo-Hittite hieroglyphic inscription. From Carchemish or Karkemish, Hittite civilization
No full textBasalt slab with neo-Hittite hieroglyphic inscription. From Carchemish or Karkemish, Hittite civilization housed in Ankara, Anadolu Medeniyetler Muzesi (Archaeological Museum), near Eastern Civilizations, Anatolian Civilization, Hittite Civilization (1650-700 B.C.), 9th-8th Century BC.Black & white photograph