A terahertz (THz) Brewster vacuum window has been developed for the newly emerged ultrabroadband gyrotron application. In the simulation, the influences of the slant angle, the thickness, and the dielectric constant of the window plate on the results were systematically analyzed. In the experimental measurement, two THz high-directivity horn antennas were used to produce and collect a quasi-plane wave that travels through the window. The measurement shows that the window transmission coefficient between 0.33 and 0.50 THz is higher than -1 dB. A conventional Brewster window uses an elliptical window plate, resulting in the asymmetrical stress distribution. In this letter, a novel circular symmetrical ceramic-Kovar brazing scheme is applied to mitigate the challenging asymmetrical stress distribution. This Brewster window would promote the development of the broadband THz gyrotron and other high-power THz systems.
Recently emerged multimode gyrotron, a high-power broadband terahertz radiator, encounters the challenge of efficiently converting a series of operating whispering-gallery modes (WGMs) into free-space Gaussian beams. To this demand, we propose a frequency- and mode-insensitive antenna capable of broadband multimode converting. For a single mode, to achieve broadband operation, special reflector configuration and large-radius launcher guarantee the system high robustness to frequency-induced wave number variation. Furthermore, for a series of operating WGMs, in order to achieve multimode operation, high-order mode indices guarantees familiar field patterns and ray trajectories. In particular, high-purity Gaussian beams are simultaneously achieved in different WGMs of broad continuous bands, including 351–361 GHz for TE11,2 mode, 375–385 GHz for TE12,2 mode, and 398–410 GHz for TE13,2 mode. The results are verified by both the vector diffraction theory and the method of momentum. This kind of mode converter will promote the development of multimode gyrotrons and other antenna-feeder systems for high-power terahertz applications.
A pair of uranyl complexes incorporating tetrahydrosalen and N,N-dimethyltetrahydrosalen ligands are synthesized and studied. These new ligands, with saturated secondary and tertiary amines, exhibit higher chemostability than the prototype Schiff base (salen) structure, especially under acidic conditions. As shown by X-ray diffraction crystallography, the coordination geometry of uranium in these new complexes is a distorted pentagonal bipyramid. Interestingly, UO2([H-4]-salen), comprising the tetrahydrosalen ligand, forms a dimeric structure in the crystals, with two subunits held together by sharing one of the two phenoxy oxygen atoms from each subunit, whereas UO2([H2Me2]-salen) with the N,N-dimethyltetrahydrosalen ligand is in the monomer state, with a solvent molecule coordinated to uranium to complete the penta-coordination configuration. Moreover, as revealed by UV/Vis spectroscopy using the colorimetry method, these hydrogenated salen ligands exhibit comparable, or even higher, binding affinities toward uranyl than the prototype Schiff base salen ligand in weakly basic solution.
In this paper, thermodynamic phase behaviour and miscibility of confined pure and mixing fluids in nanopores are studied. First, a semi-analytical equation of state (EOS) is developed, based on which two correlations are modified to predict the shifts of critical temperature and pressure. Second, the thermodynamic free energy of mixing and solubility parameter are derived, quantitatively calculated, and applied to study the conditions and characteristics of the fluid miscibility in nanopores. Third, an improved EOS model with the modified correlations is proposed and used to calculate the phase properties and miscibility-associated quantities of three mixing fluids. The critical temperature and pressure of confined fluids are always decreased by reducing the pore radius. The negative pressure state is validated for a confined liquid, whose upper temperature limit is quantitatively determined and found to be lowered with the reduction of pore radius. The liquid–gas miscibility is beneficial from the pore radius reduction and the intermediate hydrocarbons (e.g., C2, C3, i- and n-C4) perform more miscible with the liquid C8 in comparison with the lean gas (e.g., N2 and CH4). Moreover, the molecular diameter of single liquid molecule is determined to be the bottom limit, the pore radius above which is concluded as a necessary condition for the liquid–gas miscibility. The calculated phase behaviour and minimum miscibility pressures (MMPs) of the three mixing fluids agree well with the literature results, which reveals that the shifts of critical properties dominate the phase behaviour and miscibility changes of confined fluids from bulk phase to nanopores.
The earliest evidence for the Koinon of the Cities in Pontus, comprised of a group of cities in coastal Paphlagonia, is a Trajanic honorific inscription, which happens to be one of two lost "official documents – as Søren Sørensen (2016) describes them – that provide the full title of the koinon’s existence, as well as some indication that their findspots at Amastris and Heraclea were likely the metropoleis of the koinon (Sørensen 2016, p. 73- 74). Sørensen’s treatment of the two inscriptions, while brief, represents a trend in scholarship that is shifting away from the entrenched acadmic debate on the geographical extent of the elusive coastal Paphlagonian koinon, a century-long tradition which he artifully summarized as “a war of analysts and unitarians” (Sørensen 2016, p. 75-84). This paper takes a closer look at the contents of the two documents (Kalinka 1933, p. 73 no. 21; p. 95 no. 67), along with a reference to a krima issued by the koinoboulion in concert with the boule and demos of Heraclea (Kalinka 1933, p. 93 no. 69), in order to study the Koinon of the Cities in Pontus based on the information that could be elicited from the words of the koinon itself.
While the documents concerning the Koinon of the Cities in Pontus provide only snippets of its operational aspects, including the eligibility of candidates, the preferences of the koinon assembly, and deeper involvement in affairs concerning civic training and testamentary execution, they together indicate that the Koinon was likely a permanent institution that did not convene or focus its operation solely on affairs pertaining to the honoring of the emperors or the organizing of festivities, as Marek supposed in his short treatment on the matter (Marek 2003, pp. 63-67). The degree of engagement of the Koinon on
municipal affairs of its constituent communities is considerable: it took interest in the performances of its leading men in the Amastrian neoi, and it joined the boule and demos of Heraclea in honoring a citizen from Heraclea for volunteering to take up the koinon archierosyne. The invocation of the krima – a joint “opinion” of the koinoboulion and the Heraclean boule and demos – in the execution of a private will indicates that the authority of the Koinon of the Cities in Pontus was regarded as an important factor even in testamentary execution. This document in particular suggests that there must have been some degree of administrative integration between the Koinon of the Cities and its constituent communities.
These findings help integrate the Koinon of the Cities in Pontus into the recent academic discourse concerning the role in provincial administration that the koina of the Greek East played during the Principate. Jürgen Deininger’s 1965 study on koina and concilia during the Principate argued that such provincial- level institutions as primarily ceremonial, with only some diplomatic functions in addition to the worship of the emperors organization of games in the emperors’ honor. Sporadic objections since the initial publication of his work have been recently tabulated and assessed by Babett Edelmann-Singer (2015), who convincingly rejected Deininger’s limiting interpretation of evidence concerning financial and administrative aspects already available to him, and further demonstrated how Deininger’s thesis require revision in light of new epigraphical discoveries, such as the lex portorii Lyciae (Takmer 2007). As Edelmann-Singer did not touch upon the Koinon of the Cities in Pontus extensively, nor did she take note of the evidentiary value of the three documents highlighted by Sørensen, the analyses of the three documents of the Koinon of the Cities in Pontus in this paper supplements her work in exploring the various aspects that were downplayed by Deininger or unknown to him.
With MEMS technology developing rapidly, the microfluidic droplet technology has been employed into many biological or chemical experiments. To satisfy the increasingly high demands in various applications of the microfluidic chips, the size of the droplet needs accurate control. We have designed and performed a three-dimensional numerical simulation of a droplet generation in a double T-junction microchannel by a level-set method in COMSOL5.0 for discussing the process of the droplet formation and the influences on the size of the droplet. We have studied out that the flow rate ratio, the continuous phase viscosity, the interfacial tension, and the contact angle influence the size of the droplet. The effective droplet diameter increases when the flow rate ratio and the interfacial tension increase. It decreases when the continuous phase viscosity and the contact angle increase. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)
High-order mode employed as the operating mode of a terahertz (THz) gyrotron traveling-wave tube (gyro-TWT) amplifier shows strong dispersion, which deteriorates the device performance in amplifying picosecond THz pulses. Theoretical investigation of a THz gyro-TWT amplifier with a lossy cylindrical circuit is carried out to study the problems, such as lossy structure design, parameters selection, frequency-domain performance, and time-domain dynamics. The robust high growth rate low-kz amplification and the broadband high-kz amplification are two preferred operation conditions. The revealed characteristics are also useful for developing THz gyro-TWTs with other kinds of over-moded circuits.