Готові списки джерел за темами / Secondary orbital interaction

Добірка наукової літератури з теми "Secondary orbital interaction"

Автор: Grafiati

Опубліковано: 10 грудня 2022

Оновлено: 29 січня 2023

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Статті в журналах з теми "Secondary orbital interaction"

Kurita, Yasuyuki, and Chiyozo Takayama. "Secondary orbital interaction vs. orbital distortion in stereoselectivity." Tetrahedron 46, no. 11 (January 1990): 3789–802. http://dx.doi.org/10.1016/s0040-4020(01)90514-9.

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Rauw, G., A. Pigulski, Y. Nazé, A. David-Uraz, G. Handler, F. Raucq, E. Gosset, et al. "BRITE photometry of the massive post-RLOF system HD149 404." Astronomy & Astrophysics 621 (December 20, 2018): A15. http://dx.doi.org/10.1051/0004-6361/201833594.

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Context. HD 149 404 is an evolved non-eclipsing O-star binary that has previously undergone a Roche lobe overflow interaction. Aims. Understanding some key properties of the system requires a determination of the orbital inclination and of the dimensions of the components. Methods. The BRITE-Heweliusz satellite was used to collect photometric data of HD 149 404. Additional photometry was retrieved from the SMEI archive. These data were analysed using a suite of period search tools. The orbital part of the lightcurve was modelled with the nightfall binary star code. The Gaia-DR2 parallax of HD 149 404 was used to provide additional constraints. Results. The periodograms reveal a clear orbital modulation of the lightcurve with a peak-to-peak amplitude near 0.04 mag. The remaining non-orbital part of the variability is consistent with red noise. The lightcurve folded with the orbital period reveals ellipsoidal variations, but no eclipses. The minimum when the secondary star is in inferior conjunction is deeper than the other minimum due to mutual reflection effects between the stars. Combined with the Gaia-DR2 parallaxes, the photometric data indicate an orbital inclination in the range of 23°–31° and a Roche lobe filling factor of the secondary larger than or equal to 0.96. Conclusions. The luminosity of the primary star is consistent with its present-day mass, whereas the more evolved secondary appears overluminous for its mass. We confirm that the primary’s rotation period is about half the orbital period. Both features most probably stem from the past Roche lobe overflow episode.

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Raucq, F., G. Rauw, L. Mahy, and S. Simón-Díaz. "Fundamental parameters of massive stars in multiple systems: The cases of HD 17505A and HD 206267A." Astronomy & Astrophysics 614 (June 2018): A60. http://dx.doi.org/10.1051/0004-6361/201732376.

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Context. Many massive stars are part of binary or higher multiplicity systems. The present work focusses on two higher multiplicity systems: HD 17505A and HD 206267A. Aims. Determining the fundamental parameters of the components of the inner binary of these systems is mandatory to quantify the impact of binary or triple interactions on their evolution. Methods. We analysed high-resolution optical spectra to determine new orbital solutions of the inner binary systems. After subtracting the spectrum of the tertiary component, a spectral disentangling code was applied to reconstruct the individual spectra of the primary and secondary. We then analysed these spectra with the non-LTE model atmosphere code CMFGEN to establish the stellar parameters and the CNO abundances of these stars. Results. The inner binaries of these systems have eccentric orbits with e ~ 0.13 despite their relatively short orbital periods of 8.6 and 3.7 days for HD 17505Aa and HD 206267Aa, respectively. Slight modifications of the CNO abundances are found in both components of each system. The components of HD 17505Aa are both well inside their Roche lobe, whilst the primary of HD 206267Aa nearly fills its Roche lobe around periastron passage. Whilst the rotation of the primary of HD 206267Aa is in pseudo-synchronization with the orbital motion, the secondary displays a rotation rate that is higher. Conclusions. The CNO abundances and properties of HD 17505Aa can be explained by single star evolutionary models accounting for the effects of rotation, suggesting that this system has not yet experienced binary interaction. The properties of HD 206267Aa suggest that some intermittent binary interaction might have taken place during periastron passages, but is apparently not operating anymore.

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Mossoux, E., L. Mahy, and G. Rauw. "The long-period massive binary HD 54662 revisited." Astronomy & Astrophysics 615 (July 2018): A19. http://dx.doi.org/10.1051/0004-6361/201732095.

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Context. HD 54662 is an O-type binary star belonging to the CMa OB1 association. Because of its long-period orbit, this system is an interesting target to test the adiabatic wind shock model. Aims. The goal of this study is to improve our knowledge of the orbital and stellar parameters of HD 54662 and to analyze its X-ray emission to test the theoretical scaling of X-ray emission with orbital separation for adiabatic wind shocks. Methods. We applied a spectral disentangling code to a set of optical spectra to determine the radial velocities and the individual spectra of the primary and secondary stars. The orbital solution of the system was established and the reconstructed individual spectra were analyzed by means of the CMFGEN model atmosphere code. We fitted two X-ray spectra using a Markov chain Monte Carlo algorithm and compared these spectra to the emission expected from adiabatic shocks. Results. We determine an orbital period of 2103.4 days, a surprisingly low orbital eccentricity of 0.11, and a mass ratio m2/m1 of 0.84. Combined with the orbital inclination inferred in a previous astrometric study, we obtain surprisingly low masses of 9.7 and 8.2 M⊙. From the disentangled primary and secondary spectra, we infer O6.5 spectral types for both stars, of which the primary is about two times brighter than the secondary. The softness of the X-ray spectra for the two observations, the very small variation of best-fitting spectral parameters, and the comparison of the X-ray-to-bolometric luminosity ratio with the canonical value for O-type stars allow us to conclude that X-ray emission from the wind interaction region is quite low and that the observed emission is rather dominated by the intrinsic emission from the stars. We cannot confirm the runaway status previously attributed to HD 54662 by computing the peculiar radial and tangential velocities. We find no X-ray emission associated with the bow shock detected in the infrared. Conclusions. The lack of hard X-ray emission from the wind-shock region suggests that the mass-loss rates are lower than expected and/or that the pre-shock wind velocities are much lower than the terminal wind velocities. The bow shock associated with HD 54662 possibly corresponds to a wind-blown arc created by the interaction of the stellar winds with the ionized gas of the CMa OB1 association rather than by a large differential velocity between the binary and the surrounding interstellar medium.

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Gwak, Bogeun. "Coalescence of Kerr Black Holes—Binary Systems from GW150914 to GW170814." Entropy 21, no. 10 (October 20, 2019): 1017. http://dx.doi.org/10.3390/e21101017.

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We investigate the energy of the gravitational wave from a binary black hole merger by the coalescence of two Kerr black holes with an orbital angular momentum. The coalescence is constructed to be consistent with particle absorption in the limit in which the primary black hole is sufficiently large compared with the secondary black hole. In this limit, we analytically obtain an effective gravitational spin–orbit interaction dependent on the alignments of the angular momenta. Then, binary systems with various parameters including equal masses are numerically analyzed. According to the numerical analysis, the energy of the gravitational wave still depends on the effective interactions, as expected from the analytical form. In particular, we ensure that the final black hole obtains a large portion of its spin angular momentum from the orbital angular momentum of the initial binary black hole. To estimate the angular momentum released by the gravitational wave in the actual binary black hole, we apply our results to observations at the Laser Interferometer Gravitational-Wave Observatory: GW150914, GW151226, GW170104, GW170608 and GW170814.

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Politano, M., and R. F. Webbink. "The White Dwarf Mass and Orbital Period Distribution in Zero-Age Cataclysmic Binaries." International Astronomical Union Colloquium 114 (1989): 440–42. http://dx.doi.org/10.1017/s0252921100100028.

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A zero-age cataclysmic binary (ZACB) we define as a binary system at the onset of interaction as a cataclysmic variable. We present here the results of calculations of the distributions of white dwarf masses and of orbital periods in ZACBs, due to binaries present in a stellar population which has undergone continuous, constant star formation for 1010 years.Distributions of ZACBs were calculated for binaries formed t years ago, for log t = 7.4 (the youngest age at which viable ZACBs can form) to log t = 10.0 (the assumed age of the Galactic disk), in intervals of log t = 0.1. These distributions were then integrated over time to obtain the ZACB distribution for a constant rate of star formation. To compute the individual distributions for a given t, we require the density of systems forming (number of pre-cataclysmics forming per unit volume of orbital parameter space), n£(t), and the rates at which the radii of the secondary and of its Roche lobe are changing in time, s (t) and L, s (t), respectively. In calculating nf(t), we assume that the distribution of the orbital parameters in primordial (ZAMS) binaries may be written as the product of the distribution of masses of ZAMS stars (Miller and Scalo 1979), the distribution of mass ratios in ZAMS binaries (cf. Popova, et al., 1982), and the distribution of orbital periods in ZAMS binaries (Abt 1983). In transforming the the orbital parameters from progenitor (ZAMS) to offspring (ZACB) binaries, we assume that all of the orbital energy deposited into the envelope during the common envelope phase leading to ZACB formation goes into unbinding that envelope. R.L, s (t) is determined from orbital angular momentum loss rates due to gravitational radiation (Landau and Lifshitz 1951) and magnetic braking (γ = 2 in Rappaport, Verbunt, and Joss 1983). We turn off magnetic braking if the secondary is completely convective.

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Tokayer, Y. M., H. An, J. P. Halpern, J. Kim, K. Mori, C. J. Hailey, C. B. Adams, et al. "Multiwavelength Observation Campaign of the TeV Gamma-Ray Binary HESS J0632 + 057 with NuSTAR, VERITAS, MDM, and Swift." Astrophysical Journal 923, no. 1 (December 1, 2021): 17. http://dx.doi.org/10.3847/1538-4357/ac2c6a.

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Abstract HESS J0632+057 belongs to a rare subclass of binary systems that emit gamma rays above 100 GeV. It stands out for its distinctive high-energy light curve, which features a sharp “primary” peak and broader “secondary” peak. We present the results of contemporaneous observations by NuSTAR and VERITAS during the secondary peak between 2019 December and 2020 February, when the orbital phase (ϕ) is between 0.55 and 0.75. NuSTAR detected X-ray spectral evolution, while VERITAS detected TeV emission. We fit a leptonic wind-collision model to the multiwavelength spectra data obtained over the four NuSTAR and VERITAS observations, constraining the pulsar spin-down luminosity and the magnetization parameter at the shock. Despite long-term monitoring of the source from 2019 October to 2020 March, the MDM observatory did not detect significant variation in Hα and Hβ line equivalent widths, an expected signature of Be-disk interaction with the pulsar. Furthermore, fitting folded Swift-XRT light-curve data with an intrabinary shock model constrained the orbital parameters, suggesting two orbital phases (at ϕ D = 0.13 and 0.37), where the pulsar crosses the Be-disk, as well as phases for the periastron (ϕ 0 = 0.30) and inferior conjunction (ϕ IFC = 0.75). The broadband X-ray spectra with Swift-XRT and NuSTAR allowed us to measure a higher neutral hydrogen column density at one of the predicted disk-passing phases.

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Sheppard, Rachel Y., Michael T. Thorpe, Abigail A. Fraeman, Valerie K. Fox, and Ralph E. Milliken. "Merging Perspectives on Secondary Minerals on Mars: A Review of Ancient Water-Rock Interactions in Gale Crater Inferred from Orbital and In-Situ Observations." Minerals 11, no. 9 (September 9, 2021): 986. http://dx.doi.org/10.3390/min11090986.

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Phyllosilicates, sulfates, and Fe oxides are the most prevalent secondary minerals detected on Mars from orbit and the surface, including in the Mars Science Laboratory Curiosity rover’s field site at Gale crater. These records of aqueous activity have been investigated in detail in Gale crater, where Curiosity’s X-ray diffractometer allows for direct observation and detailed characterization of mineral structure and abundance. This capability provides critical ground truthing to better understand how to interpret Martian mineralogy inferred from orbital datasets. Curiosity is about to leave behind phyllosilicate-rich strata for more sulfate-rich terrains, while the Mars 2020 Perseverance rover is in its early exploration of ancient sedimentary strata in Jezero crater. It is thus an appropriate time to review Gale crater’s mineral distribution from multiple perspectives, utilizing the range of chemical, mineralogical, and spectral measurements provided by orbital and in situ observations. This review compares orbital predictions of composition in Gale crater with higher fidelity (but more spatially restricted) in situ measurements by Curiosity, and we synthesize how this information contributes to our understanding of water-rock interaction in Gale crater. In the context of combining these disparate spatial scales, we also discuss implications for the larger understanding of martian surface evolution and the need for a wide range of data types and scales to properly reconstruct ancient geologic processes using remote methods.

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Singleton, Daniel A. "A [4 + 3] transition state for a [4 + 2] cycloaddition. A new secondary orbital interaction in Diels-Alder reactions." Journal of the American Chemical Society 114, no. 16 (July 1992): 6563–64. http://dx.doi.org/10.1021/ja00042a049.

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Kashi, Amit, and Amir Michaelis. "Numerical Study of Colliding Winds in Massive Stars." Galaxies 10, no. 1 (December 28, 2021): 4. http://dx.doi.org/10.3390/galaxies10010004.

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We run a numerical experiment ejecting stellar winds in a very massive binary system measuring the properties of the resulting colliding wind structure and accreted mass onto the companion under different conditions. Colliding massive binaries interact and create a colliding wind structure with a shape that depends on the momentum ratio, orbital motion, distance between the stars, and other factors. We run simulations of a static LBV-WR binary and in each simulation abruptly varying the mass loss rate of the LBV from the fiducial value. The modified wind front propagates and interacts with the previous colliding wind structure, and modifies its shape. We calculate the emitted X-ray from the interaction and investigate the proprieties of the new shape. We derive the mass accretion rate onto the secondary, and find that it depends on the momentum ratio of the winds. We then add orbital velocity that reduces the mass accretion rate, a similar behaviour as the analytical estimates based on modified Bondi–Hoyle–Lyttleton. Creating a large set of simulations like those presented here can allow constraining parameters for specific colliding wind binaries and derive their stellar parameters and orbital solution.

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Більше джерел

Дисертації з теми "Secondary orbital interaction"

Lording, William James. "A deeper understanding of the Diels–Alder reaction." Phd thesis, 2010. http://hdl.handle.net/1885/11776.

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The Diels-Alder reaction was discovered in 1928 and has become the most efficient and practical method for the synthesis of six-membered carbocyclic and heterocyclic rings. This thesis comprises three chapters of results and discussion with the Diels-Alder reaction as a theme. Chapter 2 details an investigation of endo:exo selectivity in the Diels-Alder reactions of 1,3-butadiene. Chapter 3 explores aspects of the intramolecular Diels-Alder reactions of some substituted 1,3,8-nonatrienes, and Chapter 4 describes the domino Diels-Alder reactions of 1,4-diiodo-1,3-butadiene. The Diels-Alder reaction is powerful, general, and widely used in chemical synthesis, and it is well known that many Diels-Alder reactions exhibit endo selectivity, in accord with Alder’s empirical rule. The origins of endo:exo selectivity in the Diels-Alder reaction, however, are not completely understood and there is a dearth of experimental evidence concerning the Diels-Alder reactions of the archetypal 1,3-diene, 1,3- butadiene. Chapter 2 describes a study of the Diels-Alder reactions of an isotopically labelled 1,3-butadiene with a range of simple dienophiles, allowing the endo:exo selectivities of these important reactions to be determined for the first time. The experimental data shed light on the origins of endo:exo selectivity in the Diels-Alder reaction and will serve as an important reference for future computational investigations in this area. The intramolecular Diels-Alder reaction shares many of the virtues of its intermolecular counterpart, however its use in chemical synthesis is limited because intramolecular Diels-Alder reactivity and stereoselectivity are often governed by subtle factors, and can be very difficult to predict. As part of a comprehensive experimental and computational collaboration, Chapter 3 describes an investigation of the heat and Lewis acid promoted intramolecular Diels-Alder reactions of some ether tethered 1,3,8-nonatrienes. Also presented are the results of a rate study and a kinetic isotope effect study involving the intramolecular Diels-Alder reactions of some 1,3,8-nonatrienes. The experimental data are analysed and compared with predicted stereoselectivities, activation barriers and kinetic isotope effects obtained from computational modelling. Increased efficiency in chemical synthesis conserves resources, reduces waste, and saves time and money. Domino reactions are particularly efficient processes, which can generate complex products from simple reactants. Chapter 4 describes an investigation of the domino Diels-Alder reactions of (1E,3E)-1,4-diiodo-1,3-butadiene with maleimide dienophiles, through which a family of bicyclo[2.2.2]oct-2-ene derivatives are produced in one high yielding and stereoselective synthetic step.

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Частини книг з теми "Secondary orbital interaction"

Sapse, Anne-Marie. "Ab Initio Studies of Anti-Cancer Drugs." In Molecular Orbital Calculations for Biological Systems. Oxford University Press, 1998. http://dx.doi.org/10.1093/oso/9780195098730.003.0011.

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Cancer is an extraordinarily complicated group of diseases which are characterized by the loss of normal control of the maintenance of cellular organization in the tissues. It is still not completely understood how much of the disease is of genetic, viral, or environmental origin. The result, however, is that cancer cells possess growth advantages over normal cells, a reality which damages the host by local pressure effects, destruction of tissues, and secondary systemic effects. As such, a goal of cancer therapy is the destruction of cancer cells via chemotherapeutic agents or radiation. Since the late 1940s, when Farber treated leukemia with methotrexate, cancer therapy with cytotoxic drugs made enormous progress. Chemotherapy is usually integrated with other treatments such as surgery, radiotherapy, and immunotherapy, and it is clear that post-surgery, it is effective with solid tumors. This is due to the fact that only systemic therapy can attack micrometastases. The rationale for using chemotherapy is the control of tumor-cell populations via a killing mechanism. The major problem in this approach is the lack of selectivity of chemotherapeutic agents. Some agents indeed preferentially kill cancer cells, but no agents have been synthesized yet which kill only cancer cells and do not affect normal cells. Unfortunately, normal tissues are affected, giving rise to a multitude of side effects. In addition to drugs exhibiting cytotoxic activity, antiproliferative drugs are also formulated. According to their mode of action, anti-cancer drugs are divided into several classes. . . . alkylating agents antimetabolites DNA intercalators mitotic inhibitors lexitropsins drugs which bind covalently to DNA . . . Experimental studies of these molecules are complemented and enhanced by theoretical studies. Some of the theoretical studies use molecular mechanics methods while others apply ab initio or semi-empirical quantum-chemistry methods. Most of these molecules are large and besides their structures and properties it is important to investigate their interaction with DNA fragments (themselves large molecules). Ab initio calculations cannot always be applied to the whole system. Therefore, models are used and through a judicious choice of the entities investigated, the calculations can shed light on the problem and provide enough information to complement the experimental studies.

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Szabo, Arthur G. "Fluorescence principles and measurement." In Spectrophotometry and Spectrofluorimetry. Oxford University Press, 2000. http://dx.doi.org/10.1093/oso/9780199638130.003.0006.

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Fluorescence spectrometry is the most extensively used optical spectroscopic method in analytical measurement and scientific investigation. During the past five years more than 60000 scientific articles have been published in which fluorescence spectroscopy has been used. The large number of applications ranges from the analytical determination of trace metals in the environment to pH measurements in whole cells under physiological conditions. In the scientific research laboratory, fluorescence spectroscopy is being used or applied to study the fundamental physical processes of molecules; structure-function relationships and interactions of biomolecules such as proteins and nucleic acids; structures and activity within whole cells using such instrumentation as confocal microscopy; and DNA sequencing in genomic characterization. In analytical applications the use of fluorescence is dominant in clinical laboratories where fluorescence immunoassays have largely replaced radioimmunoassay techniques. There are two main reasons for this extensive use of fluorescence spectroscopy. Foremost is the high level of sensitivity and wide dynamic range that can be achieved. There are a large number of laboratories that have reported single molecule detection. Secondly, the instrumentation required is convenient and for most purposes can be purchased at a modest cost. While improvements and advances continue to be reported fluorescence instrumentation has reached a high level of maturity. A review of the physical principles of the fluorescence phenomenon permits one to understand the origins of the information content that fluorescence measurements can provide. A molecule absorbs electromagnetic radiation through a quantum mechanical process where the molecule is transformed from a ‘ground’ state to an ‘excited’ state. The energy of the absorbed photon of light corresponds to the energy difference between these two states. In the case of light in the ultraviolet and visible spectral range of 200 nm to 800 nm that corresponds to energies of 143 to 35.8 kcal mol-1. The absorption of light results in an electronic transition in the atom or molecule. In atoms this involves the promotion of an electron from an outer shell orbital to an empty orbital of higher energy.

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Linberg, John V. "Evaluation of the Lacrimal System." In Surgery of the Eyelid, Lacrimal System, and Orbit. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780195340211.003.0019.

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The common complaint of a watering eye may be caused by a variety of problems, including lacrimal hyposecretion, lacrimal hypersecretion, or blockage of the lacrimal drainage system. This system is a complex membranous channel whose function depends on the interaction of anatomy and physiology. Effective tear drainage depends on a variety of factors, including the volume of tear secretion, eyelid position, and anatomy of the lacrimal drainage passages. Epiphora is defined as an abnormal overflow of tears down the cheek. The patient with symptomatic tearing may have a normal lacrimal drainage system overwhelmed by primary or secondary (reflex) hypersecretion or a drainage system that is anatomically compromised and unable to handle normal tear production. On the other hand, a patient with partial drainage obstruction may have a concomitant reduction in tear production and therefore be completely asymptomatic or may even suffer from symptomatic dry eye syndrome. Epiphora is determined by the balance between tear production and tear drainage, not by the absolute function or dysfunction of either one. The causes of lacrimal drainage problems can be divided into two categories: anatomic and functional. Anatomic obstruction refers to a mechanical or structural abnormality of the drainage system. The obstruction may be complete, such as punctal occlusion, canalicular blockage, or nasolacrimal duct fibrosis, or partial, caused by punctal stenosis, canalicular stenosis, or mechanical obstruction within the lacrimal sac (i.e., dacryolith or tumor). In patients with functional obstruction, epiphora results not from anatomic blockage but from a failure of lacrimal drainage physiology. This failure may be caused by anatomic deformity such as punctal eversion or other eyelid malpositions, but can also result from lacrimal pump inadequacy caused by weak orbicularis muscle action. It is helpful to determine whether the patient’s complaint is true epiphora or a “watery eye.” Detailed history-taking and careful examination will help direct the evaluation of a tearing eye. A host of clinical tests have been described, and the selection of appropriate tests will depend on the initial history and ophthalmic examination. 13-1-1 History-Taking. Any clinical evaluation should begin with a thorough history. A complaint of watery eye does not necessarily imply a lacrimal drainage problem.

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"into account. Therefore, every time a new batch of food is to be irradiated, the operator must establish the dose and dose distribution by strategically placing dose meters into and between the food packages and evaluating the dose meter reading. Once the process is running smoothly, it is usually not necessary to carry out dosimetry on all the product. Monitoring the process parameters and making occasional dosimetric checks is now sufficient (23). In most countries government regulations require that food irradiation proces sors maintain records that describe for each food lot the radiation source, source calibration, dosimetry, dose distribution in the product, and certain other process parameters (see Chapter 11). A short introduction to the interaction of ionizing radiation with matter is appro priate at this point, although the effects of ionizing radiation on food components will be described in more detail in Chapter 3. When high-energy electrons are absorbed by a medium they lose their kinetic energy by interacting with electrons of the medium. (At very high energy, far above that allowed for food irradiation, accelerated electrons can also interact with nuclei of the medium.) The interaction with orbital electrons of the atoms of the medium (the absorber) causes ionizations and excitations. Ionization means that orbital electrons are ejected from atoms of the medium; excitation means that orbital electrons move to an orbit of higher energy. Ejected electrons (secondary electrons), carrying a large portion of the energy of the incident electron, also lose energy through interaction with orbital electrons of the absorber. Electrons at low velocities (subexcitation energy level) can cause molecular vibrations on their way to becoming thermalized. As a result of the collisions with atoms of the absorber material the incident electrons can change direction. Repeated collisions cause multiple changes of direction. The result is a scattering of electrons in all directions. This is shown schematically in Figure 12a. When gamma or x-ray photons interact with the absorber, three types of interaction can occur: The photoelectric effect The Compton effect, and Pair production (i.e., formation of pairs of electrons and positrons) Photoelectric absorption occurs largely with photons of energies below 0.1 MeV and pair production primarily with photons of energies above 10 MeV. Both are of minor importance in food irradiation, where the Compton effect predominates. As portrayed in Figure 13, in the Compton effect an incident photon interacts with an absorber atom in such a way that an orbital electron is ejected. The incident photon continues after the collision in a changed direction and with less." In Safety of Irradiated Foods, 47–48. CRC Press, 1995. http://dx.doi.org/10.1201/9781482273168-37.

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Тези доповідей конференцій з теми "Secondary orbital interaction"

Oh, Sejoong, Karl Grosh, and James R. Barber. "Dynamic Stability Analysis of Spur Gears in a Steady State." In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0194.

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Abstract In the previous work by the authors (Oh et al. (1998)), it was shown that in order for the model of an interacting spur gear pair to conserve energy, the dependence of the mesh stiffness on the mean rotation must be included in deriving the equations of motion. A quadratic nonlinearity arises from the dependence of the mesh stiffness on the mean rotation, even under the assumption of small deflection. This nonlinearity ensures conservation of energy. In this study, the stability of the steady-state response of interacting spur gears, both for the new equation of motion (EOM) and the classical EOM, is investigated. The map for periodic orbits is determined and a linearized stability analysis is performed. Once the stability is determined, the comparison between the classical and the new EOM is made for a primary, a secondary sub-harmonic, and super-harmonic resonances. The frequency-amplitude curve from direct simulation is compared to the stability analysis. The effect on the stability by the nonlinear jump term is shown, as well as by the variable time. The effect of damping and the magnitude of the applied torque on the stability is shown.

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Stutz, Colin, Douglas Bohl, and Melissa Green. "Wake Properties of an Oscillating Airfoil Undergoing Small Amplitude Asymmetric Oscillation." In ASME 2020 Fluids Engineering Division Summer Meeting collocated with the ASME 2020 Heat Transfer Summer Conference and the ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/fedsm2020-20360.

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Abstract The flow around, and in the wake of, pitching airfoils has received renewed interest due to its potential for thrust production at low Reynolds numbers. Past work has centered on the flow fields generated by symmetric pitching of the airfoil. Studies investigating the effects of asymmetric motion are more limited. This work focuses on the wake patterns developed due to asymmetric pitching. Particle Image Velocimetry (PIV) is used to quantify the flow field around a NACA0012 airfoil undergoing small amplitude, high frequency asymmetric pitching. The airfoil is pitched about the quarter chord point with an amplitude of ±4° at reduced frequencies of k = 2.6–5.8 at a Rec = 12000. Pitching symmetries of 50/50, 40/60 and 30/70 are studied, where the symmetry is defined by the fraction of the cycle spent in the pitch down versus pitch up motion. The data show that for the 50/50 (symmetric) motions two alternating sign vortices, with equivalent strength, are formed as expected. The asymmetric cases show that a single vortex is formed during the “fast” portion of the pitching motion. Multiple vortices are formed during the “slow” portion of the pitching motion. The number of secondary vortices and the downstream evolution of the vortices depends on the symmetry value. In some cases they remain isolated but orbit other vortical structures, while in other cases they pair with other vortical structures, and finally when the reduced frequency and asymmetry values are high enough the vortex array shows interaction between cycles.

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