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441.
The problem of scattering of airborne sound by a dynamically rough surface of a turbulent, open channel flow is poorly understood. In this work, a laser-induced fluorescence (LIF) technique is used to capture accurately a representative number of the instantaneous elevations of the dynamically rough surface of 6 turbulent, subcritical flows in a rectangular flume with Reynolds numbers of 10,800?Re?47,300 and Froude numbers of 0.36?Fr?0.69. The surface elevation data were then used in a finite difference time domain (FDTD) model to predict the directivity pattern of the airborne sound pressure scattered by the dynamically rough flow surface. The predictions obtained with the FDTD model were compared against the sound pressure data measured in the flume and against that obtained with the Kirchhoff approximation. It is shown that the FDTD model agrees with the measured data within 22.3%. The agreement between the FDTD model and stationary phase approximation based on Kirchhoff integral is within 3%. The novelty of this work is in the direct use of the LIF data and FDTD model to predict the directivity pattern of the airborne sound pressure scattered by the flow surface. This work is aimed to inform the design of acoustic instrumentation for non-invasive measurements of hydraulic processes in rivers and in partially filled pipes. 相似文献
442.
Oleg G. Salnikov Dr. Danila A. Barskiy Dr. Aaron M. Coffey Dr. Kirill V. Kovtunov Prof. Igor V. Koptyug Prof. Eduard Y. Chekmenev 《Chemphyschem》2016,17(21):3395-3398
We report on a simple approach for efficient NMR proton hyperpolarization of propane using the parahydrogen‐induced polarization (PHIP) technique, which yielded ≈6.2 % proton polarization using ≈80 % parahydrogen, a record level achieved with any hyperpolarization technique for propane. Unlike in previously developed approaches designed for continuous‐flow operation, where reactants (propene and parahydrogen) are simultaneously loaded for homogeneous or heterogeneous pairwise addition of parahydrogen, here a batch‐mode method is applied: propene is first loaded into the catalyst‐containing solution, which is followed by homogeneous hydrogenation via parahydrogen bubbling delivered at ≈7.1 atm. The achieved nuclear spin polarization of this contrast agent potentially useful for pulmonary imaging is approximately two orders of magnitude greater than that achieved in the continuous‐flow homogeneous catalytic hydrogenation, and a factor of 3–10 more efficient compared to the typical results of heterogeneous continuous‐flow hydrogenations. 相似文献
443.
Natalia A. Shnayder Marina M. Petrova Tatiana E. Popova Tatiana K. Davidova Olga P. Bobrova Vera V. Trefilova Polina S. Goncharova Olga V. Balberova Kirill V. Petrov Oksana A. Gavrilyuk Irina A. Soloveva German V. Medvedev Regina F. Nasyrova 《Molecules (Basel, Switzerland)》2021,26(9)
Chronic pain syndromes are an important medical problem generated by various molecular, genetic, and pathophysiologic mechanisms. Back pain, neuropathic pain, and posttraumatic pain are the most important pathological processes associated with chronic pain in adults. Standard approaches to the treatment of them do not solve the problem of pain chronicity. This is the reason for the search for new personalized strategies for the prevention and treatment of chronic pain. The nitric oxide (NO) system can play one of the key roles in the development of peripheral pain and its chronicity. The purpose of the study is to review publications devoted to changes in the NO system in patients with peripheral chronical pain syndromes. We have carried out a search for the articles published in e-Library, PubMed, Oxford Press, Clinical Case, Springer, Elsevier, and Google Scholar databases. The search was carried out using keywords and their combinations. The role of NO and NO synthases (NOS) isoforms in peripheral pain development and chronicity was demonstrated primarily from animal models to humans. The most studied is the neuronal NOS (nNOS). The role of inducible NOS (iNOS) and endothelial NOS (eNOS) is still under investigation. Associative genetic studies have shown that single nucleotide variants (SNVs) of NOS1, NOS2, and NOS3 genes encoding nNOS, iNOS, and eNOS may be associated with acute and chronic peripheral pain. Prospects for the use of NOS inhibitors to modulate the effect of drugs used to treat peripheral pain syndrome are discussed. Associative genetic studies of SNVs NOS1, NOS2, and NOS3 genes are important for understanding genetic predictors of peripheral pain chronicity and development of new personalized pharmacotherapy strategies. 相似文献
444.
Dr. Kirill F. Sheberstov Vitaly P. Kozinenko Dr. Alexey S. Kiryutin Prof. Hans-Martin Vieth Herbert Zimmermann Prof. Konstantin L. Ivanov Dr. Alexandra V. Yurkovskaya 《Chemphyschem》2021,22(14):1527-1534
The development of nuclear spins hyperpolarization, and the search for molecules that can be efficiently hyperpolarized is an active area in nuclear magnetic resonance. In this work we present a detailed study of SABRE SHEATH (signal amplification by reversible exchange in shield enabled alignment transfer to heteronuclei) experiments on 15N2-azobenzene. In SABRE SHEATH experiments the nuclear spins of the target are hyperpolarized through transfer of spin polarization from parahydrogen at ultralow fields during a reversible chemical process. Azobenzene exists in two isomers, trans and cis. We show that all nuclear spins in cis-azobenzene can be efficiently hyperpolarized by SABRE at suitable magnetic fields. Enhancement factors (relative to 9.4 T) reach up to 3000 for 15N spins and up to 30 for the 1H spins. We compare two approaches to observe either hyperpolarized magnetization of 15N/1H spins, or hyperpolarized singlet order of the 15N spin pair. The results presented here will be useful for further experiments in which hyperpolarized cis-15N2-azobenzene is switched by light to trans-15N2-azobenzene for storing the produced hyperpolarization in the long-lived spin state of the 15N pair of trans-15N2-azobenzene. 相似文献
445.
Dr. Sergey V. Baykov Kirill K. Geyl Dr. Daniil M. Ivanov Dr. Rosa M. Gomila Prof. Dr. Antonio Frontera Prof. Dr. Vadim Y. Kukushkin 《化学:亚洲杂志》2021,16(11):1445-1455
An interplay between 4-bromo- and 4-iodo-5-nitrophthalonitriles (XNPN, X=Br or I) and any one of the azines (pyridine 1 , 4-dimethylaminopyridine 2 , isoquinoline 3 , 4-cyanopyridine 4 , 2-methylpyridine 5 , 2-aminopyridine 6 , quinoline 7 , 1-methylisoquinoline 8 , and 2,2’-bipyridine 9 ) proceeds differently depending on steric and electronic effects of the heterocycles. Sterically unhindered azines 1–3 underwent N-arylation to give the corresponding azinium salts (characterized by 1H and 13C{H} NMR and high-resolution ESI-MS). In contrast, azines 4 – 9 with sterically hindered N atoms or bearing an electron-withdrawing substituent, form stable co-crystals with XNPN, where two interacting molecules are bound by halogen bonding. In all obtained co-crystals, X⋅⋅⋅N structure-directed halogen bonds were recognized and theoretically evaluated including DFT calculations (PBE0-D3/def2-TZVP level of theory), QTAIM analysis, molecular electrostatic potential surfaces, and noncovalent interaction plot index. Estimated energies of halogen bonding vary from −7.6 kcal/mol (for 6 ⋅ INPN) to −11.4 kcal/mol ( 5 ⋅ INPN). 相似文献
446.
A tricyclic core structure 2 related to gelsemine 1 was synthesized from an oxabicyclo[3.2.1]octanone 4 by a three-step bridge swapping strategy involving elimination of the bridging ether oxygen and intramolecular Michael addition of a tethered cyanoacetamide unit. 相似文献
447.
Velizhanin KA Kilina S Sewell TD Piryatinski A 《The journal of physical chemistry. B》2008,112(42):13252-13257
Numerical studies of vibrational energy transport and associated (non)linear infrared and Raman response in polyatomic materials require knowledge of the multidimensional vibrational potential-energy surface and the ability to perform normal-mode analysis on that potential. The presence of translational symmetry, as in crystals, leads to the observed dispersion of the unit cell normal modes and has to be accounted for in calculations of energy transfer rates and other spectroscopic quantities. Here we report on the implementation of a computational approach that combines the generalized supercell method and density functional theory electronic structure calculations to investigate the vibrational structure in translationally symmetric materials containing relatively large numbers of atoms in the unit cell (58 atoms in the present study). The method is applied to calculate the phonon and vibron dispersion relations and the vibrational density of states in pentaerythritol tetranitrate (PETN) molecular crystal which is an important energetic material. The results set the stage for future investigations of vibrational energy transport and associated nonlinear spectroscopic signatures in this class of materials. 相似文献
448.
Kirill V. Zaitsev Yuri F. Oprunenko Judith A.K. Howard Galina S. Zaitseva 《Journal of organometallic chemistry》2008,693(1):173-179
Novel substituted 2-[(2-hydroxyethyl)]aminophenols, MeN(CHR1CR2R3OH)(C6H4-o-OH) (2-5), were synthesized by the reaction of 2-methylaminophenol with corresponding oxiranes. Titano-spiro-bis(ocanes) [MeN(CHR1CR2R3O)(C6H4-o-O)]2Ti 6-9 (2, 6, R1 = H, R2 = R3 = Me; 3, 7, R1 = R2 = Ph (treo-), R3 = H; 4, 8, R1 = Ph, R2 = R3 = H; 5, 9, R1 = R2 = H, R3 = Ph) based on [ONO]-ligands have been synthesized. The obtained compounds were characterized by 1H and 13C NMR spectroscopy and elemental analysis data. The complex [Ti(μ2-O){O-o-C6H4}{μ2-CMe2CH2}NMe]6 (10) was obtained by controlled hydrolysis of 6. Molecular structure of 10 was determined by X-ray structure analysis. 相似文献
449.
A simple one-step synthesis of a new class of fluorinated heterocycles, 4-fluoro-3-oxazolines, from diarylmethanimines, trifluoroacetophenones and CF2Br2 is described. The reaction proceeds via the sequential formation of difluorocarbene and a gem-difluorosubstituted NH-azomethine ylide, followed by 1,3-dipolar cycloaddition with a ketone. 相似文献
450.
Kirill?F.?Sheberstov Hans-Martin?Vieth Herbert?ZimmermannEmail author Konstantin?L.?Ivanov Alexey?S.?Kiryutin Alexandra?V.?YurkovskayaView authors OrcID profile 《Applied magnetic resonance》2018,49(3):293-307
We provide a detailed evaluation of nuclear magnetic resonance (NMR) parameters of the cis- and trans-isomers of azobenzene (AB). For determining the NMR parameters, such as proton–proton and proton–nitrogen J-couplings and chemical shifts, we compared NMR spectra of three different isotopomers of AB: the doubly 15N labeled azobenzene, 15N,15N′-AB, and two partially deuterated AB isotopomers with a single 15N atom. For the total lineshape analysis of NMR spectra, we used the recently developed ANATOLIA software package. The determined NMR parameters allowed us to optimize experiments for investigating singlet long-lived spin states (LLSs) of 15N spin pairs and to measure LLS lifetimes in cis-AB and trans-AB. Magnetization-to-singlet-to-magnetization conversion has been performed using the SLIC and APSOC techniques, providing a degree of conversion up to 17 and 24% of the initial magnetization, respectively. Our approach is useful for optimizing the performance of experiments with singlet LLSs; such LLSs can be exploited for preserving spin hyperpolarization, for probing slow molecular dynamics, slow chemical processes and also slow transport processes. 相似文献