34 research outputs found
Effect of base–acid properties of the mixtures of water with methanol on the solution enthalpy of selected cyclic ethers in this mixture at 298.15 K
The enthalpies of solution of cyclic ethers: 1,4-
dioxane, 12-crown-4 and 18-crown-6 in the mixture of
water and methanol have been measured within the whole
mole fraction range at T = 298.15 K. Based on the obtained
data, the effect of base–acid properties of water–
methanol mixtures on the solution enthalpy of cyclic ethers
in these mixtures has been analyzed. The solution enthalpy
of cyclic ethers depends on acid properties of water–
methanol mixtures in the range of high and medium water
contents in the mixture. Based on the analysis performed, it
can be assumed that in the mixtures of high methanol
contents, cyclic ethe
Ultraviolet astronomical spectrograph calibration with laser frequency combs from nanophotonic waveguides
Astronomical precision spectroscopy underpins searches for life beyond Earth,
direct observation of the expanding Universe and constraining the potential
variability of physical constants across cosmological scales. Laser frequency
combs can provide the critically required accurate and precise calibration to
the astronomical spectrographs. For cosmological studies, extending the
calibration with such astrocombs to the ultraviolet spectral range is highly
desirable, however, strong material dispersion and large spectral separation
from the established infrared laser oscillators have made this exceedingly
challenging. Here, we demonstrate for the first time astronomical spectrograph
calibrations with an astrocomb in the ultraviolet spectral range below 400 nm.
This is accomplished via chip-integrated highly nonlinear photonics in
periodically-poled, nano-fabricated lithium niobate waveguides in conjunction
with a robust infrared electro-optic comb generator, as well as a
chip-integrated microresonator comb. These results demonstrate a viable route
towards astronomical precision spectroscopy in the ultraviolet and may
contribute to unlocking the full potential of next generation ground- and
future space-based astronomical instruments
2023 Astrophotonics Roadmap: pathways to realizing multi-functional integrated astrophotonic instruments
This is the final version. Available on open access from IOP Publishing via the DOI in this recordData availability statement:
The data that support the findings of this study are available upon reasonable request from the authors.Photonic technologies offer numerous functionalities that can be used to realize astrophotonic instruments. The most spectacular example to date is the ESO Gravity instrument at the Very Large Telescope in Chile that combines the light-gathering power of four 8 m telescopes through a complex photonic interferometer. Fully integrated astrophotonic devices stand to offer critical advantages for instrument development, including extreme miniaturization when operating at the diffraction-limit, as well as integration, superior thermal and mechanical stabilization owing to the small footprint, and high replicability offering significant cost savings. Numerous astrophotonic technologies have been developed to address shortcomings of conventional instruments to date, including for example the development of photonic lanterns to convert from multimode inputs to single mode outputs, complex aperiodic fiber Bragg gratings to filter OH emission from the atmosphere, complex beam combiners to enable long baseline interferometry with for example, ESO Gravity, and laser frequency combs for high precision spectral calibration of spectrometers. Despite these successes, the facility implementation of photonic solutions in astronomical instrumentation is currently limited because of (1) low throughputs from coupling to fibers, coupling fibers to chips, propagation and bend losses, device losses, etc, (2) difficulties with scaling to large channel count devices needed for large bandwidths and high resolutions, and (3) efficient integration of photonics with detectors, to name a few. In this roadmap, we identify 24 key areas that need further development. We outline the challenges and advances needed across those areas covering design tools, simulation capabilities, fabrication processes, the need for entirely new components, integration and hybridization and the characterization of devices. To realize these advances the astrophotonics community will have to work cooperatively with industrial partners who have more advanced manufacturing capabilities. With the advances described herein, multi-functional integrated instruments will be realized leading to novel observing capabilities for both ground and space based platforms, enabling new scientific studies and discoveries.National Science Foundation (NSF)NAS
Association equilibria of alkyl derivatives of urea and thiourea
The studies and comparison of a series of molecular mono- and di-substituted
derivatives of urea and thiourea in solvents of increasing polarity are presented [1–4].
These substances are characterized by a high tendency to self-associate through the
formation of intermolecular hydrogen bonds due to the presence in their structure
both groups as donors (NH) as well as proton acceptors (C=O) or (C=S). Studies were
performed by using IR spectroscopy, method of measuring the average molecular
weight and the dipole moments. The experimental data were verified by DFT quantum
chemical calculations with B3PW91 correlation functional. Simultaneous use of
these techniques alowed establishing not only the efficiency of aggregation, but also
the structure and polarity of formed aggregates. It was shown, that in solvents with
weak acidic C-H groups the aggregation was strongly limited because of molecular
interactions between solute and solvent.
The theoretical DFT calculations which included the impact of the environment
on the nature of interactions in the complex were carried out [e.g. Scheme 4.1.4].
A combination of geometry optimization in polarizable continuum model (PCM)
with the connection of chloroform molecules (1,2-dichloroethane) with urea dimers
enabled to obtain the expected theoretical simulation compliance with the experiment.
The equilibrium constants were calculated on the basis of data obtained in two
independent methods of measurement: IR spectroscopy and measurements of average
molecular weights. Good agreement of experimental data of both research techniques
were found up to concentration of 0.03 mol/dm3 [Fig. 2.5]. The type of associates have
been assessed following the dipole moments measured as a function of concentration,
and on the results of density-functional theory (DFT) calculations on the structure
and energy of particular species. All of the urea derivatives demonstrated an increase
in dipole moment with increased concentration, suggesting linear-type aggregation
[Fig. 4.1.3]. Contrastingly, the dipole moments of the N,N-dimethylthiourea and
mono-N-alkyl-substituted thioureas decreased with concentration and suggest that
cyclic dimers or trimers are formed by C=S…(HR)2N-C=S interactions [Fig. 4.2.2].
The efficiency of self-aggregation was described by use of two equilibrium constants.
The first constant, K1, was describing dimer formation and the second constant, K2,
the subsequent multimer formation. In N,N’-thioureas aggregation was lower than
for the related urea compounds [Table 4.1.1 and Table 4.2.1].
Differences between urea and thiourea derivatives result from the fact that the
ureas are stronger bases and, therefore, more active in aggregation
Resonant Supercontinuum Generation in Normal and Anomalous Dispersion
We demonstrate broadband resonant supercontinuum generation based on stable bright soliton formation in Si3N4 microresonators with either anomalous or normal dispersion. The frequency combs have an electronically detectable repetition rate of 28 GHz, and span over 2,000 comb teeth
Determination of gamma angular distribution from the shape of spectral line for the first excited state of carbon nucleus
An experiment investigating gamma emission in hadron therapy was performed at Cyclotron Centre Bronowice (CCB), Cracow, Poland, using two different phantom materials—carbon and poly(methyl methacrylate) PMMA. The measurements were carried out at 70 MeV proton beam energy and the gamma quanta were registered with the use of HP Ge detector with scintillation anti-Compton shielding. Although the primary aim was to establish a solid experimental data base for future applications in prompt gamma imaging, the data have also been analyzed with regards to the position and shape of the spectral line stemming from deexcitation of the carbon excited state 4.44 MeV. Measurements potentially useful to determine the cross section were performed only at 90° laboratory polar angle. However, benefiting from the very good energy resolution it turned out possible to extract information on angular distribution of the C* (4.44 MeV) deexcitation by analyzing the associated line shape. This paper presents the scheme of model calculations assuming the whole process can be divided into two stages: excitation of carbon nuclei by impinging protons and deexcitation of the C* (4.44 MeV) state