Regions of stability of high-power gyrotron oscillators

The problem of mode competition in a high-power gyrotron oscillator is considered. The regions of parameter space in which a preexisting large-amplitude mode is able to suppress competing satellites are determined for cases in which the coupling coefficients and cavity quality factors for the operating and satellite modes are different. In addition, the effect of beam quality on the regimes of stable single-mode operation is investigated. Generally speaking, the requirement of stable operation favors devices whose interaction length measured by the parameter μ is not too large. It is found that for μ near 10 the operation is relatively stable and μ near 17 is not     

The gravitational path integral and the trace of the diffeomorphisms

I give a resolution of the conformal mode divergence in the Euclidean gravitational path-integral by isolating the trace of the diffeomorphisms and its contribution to the Faddeev-Popov measure.     

Nondestructive characterization of musical pillars of Mahamandapam of Vitthala Temple at Hampi, India

This paper presents the first scientific investigation on the musical pillars of the Vitthala Temple at Hampi, India. The solid stone columns in these pillars produce audible sound, when struck with a finger. Systematic investigations on the acoustic characteristics of the musical pillars of mahamandapam (great stage) of the Vitthala Temple have been carried out. The 11 most popular pillars that produce sounds of specific musical instruments are considered for the investigations. The sound produced from these 11 most popular musical pillars was recorded systematically and different nondestructive testing techniques such as low frequency ultrasonic testing, impact echo testing, and in situ metallography were employed on the musical columns of these pillars. The peak frequencies in the amplitude spectrum of the sound produced from various columns in these pillars are correlated with the dimensional measurements and ultrasonic velocity determined using impact echo technique. The peak frequencies obtained experimentally have been found to have excellent correlation with the calculated flexural frequencies based on the dimensional measurements and ultrasonic velocities of the columns.     

Zinc(II) mediated imine-enamine tautomerization

Reduction of imine-anthracenone compounds selectively produces secondary alcohols leaving the external imine group unreacted. Addition of the Zn(II) ion induces a metal-mediated imine-enamine tautomerization reaction that is selective for Zn(II), a new fluorescence detection method not previously observed for this important cation.     

Polyhydrazide-Based Organic Nanotubes as Efficient and Selective Artificial Iodide Channels

Reported herein is a series of pore-containing polymeric nanotubes based on a hydrogen-bonded hydrazide backbone. Nanotubes of suitable lengths, possessing a hollow cavity of about a 6.5 Å diameter, mediate highly efficient transport of diverse types of anions, rather than cations, across lipid membranes. The reported polymer channel, having an average molecular weight of 18.2 kDa and 3.6 nm in helical height, exhibits the highest anion-transport activities for iodide (EC₅₀=0.042 μm or 0.028 mol % relative to lipid), whcih is transported 10 times more efficiently than chlorides (EC₅₀=0.47 μm ). Notably, even in cholesterol-rich environment, iodide transport activity remains high with an EC₅₀ of 0.37 μm . Molecular dynamics simulation studies confirm that the channel is highly selective for anions and that such anion selectivity arises from a positive electrostatic potential of the central lumen rendered by the interior-pointing methyl groups.     

Testing primitivity on partial words

Primitive words, or strings over a finite alphabet that cannot be written as a power of another string, play an important role in numerous research areas including formal language theory, coding theory, and combinatorics on words. Testing whether or not a word is primitive can be done in linear time in the length of the word. Indeed, a word is primitive if and only if it is not an inside factor of its square. In this paper, we describe a linear time algorithm to test primitivity on partial words which are strings that may contain a number of “do not know” symbols. Our algorithm is based on the combinatorial result that under some condition, a partial word is primitive if and only if it is not compatible with an inside factor of its square. The concept of special, related to commutativity on partial words, is foundational in the design of our algorithm. A World Wide Web server interface at http://www.uncg.edu/mat/primitive/ has been established for automated use of the program.     

Enhanced dielectric and electrical performance of phosphonic acid-modified tantalum (Ta)-doped potassium sodium niobate (KNaNbO3)-P(VDF-HFP) composites

The European Physical Journal E - We discuss the lateral dynamics of two active force dipoles, which interact with each other via hydrodynamic interactions in a thin fluid layer that is active and...     

100-150 MW designs of two- and three-cavity gyroklystron amplifiersoperating at the fundamental and second harmonics in X- andKu-bands

Efficient 100-150 MW X- and Ku-band microwave sources with pulselengths of 1 μs are being developed for driving future linear colliders. Two- and three-cavity co-axial designs of relativistic gyroklystron amplifiers are presented here which fulfill these requirements. Numerical simulations predict over 40% efficiency, 45-50 dB gain, and 100-160 MW power level for the gyroklystron designs operating at fundamental (8.568 GHz) and second harmonic (17.136 GHz). It is shown that introducing a penultimate (buncher) cavity significantly improves efficiency and gain of the second-harmonic amplifier