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Neroev, V. V.; Iomdina, E. N.; Khandzhyan, A. T.; Khodzhabekyan, N. V.; Sengaeva, M. D.; Ivanova, A. V.; Seliverstov, S. V.; Teplyakova, K. O.; Goltsman, G. N. |
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Experimental study of the effect of corneal hydration and its biomechanical properties on the results of photorefractive keratectomy |
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Journal Article |
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Year |
2021 |
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Vestn. Oftalmol. |
Abbreviated Journal |
Vestn. Oftalmol. |
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137 |
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3 |
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68-75 |
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THz scanning, cornea, photorefractive keratectomy, medicine |
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Abstract |
Water content in the cornea may affect the outcome of its excimer laser ablation, especially in presbyopic patients with myopic refraction. This hypothesis can be tested by scanning the cornea in the terahertz (THz) range to determine its hydration level.
Purpose: To study the effect of hydration of the cornea determined by non-contact THz scanning and its biomechanical parameters on the results of photorefractive keratectomy (PRK) in an experiment.
Material and methods: PRK was performed using the Nidek EC-5000 QUEST excimer laser on 8 rabbit eyes. Corneal hydration was evaluated by determining the reflection coefficient (RC) in the THz electromagnetic radiation range before PRK, after 3-5 days, and after 1, 2, 3, and 4 months. Clinical examination included autorefractometry, assessment of corneal thickness and other anatomical and optical parameters of the anterior eye segment (Galilei G6, Ziemer Ophthalmic Systems AG 6.0.2, Switzerland), measurement of corneal hysteresis (CH) and corneal resistance factor (CRF) using the Ocular Response Analyzer (ORA; Reichert, USA), as well as tear production (Schirmer test).
Results: The initial water content in the cornea has a significant effect on the thickness of the removed layer, i.e. on the PRK effect, with correlation coefficient of Rs= -0.976 (p<0.01). The correlation between CH and the ablation depth is less pronounced (Rs=0.643), and CRF had no correlation with it (Rs= -0.089). Biomechanical indicators of the cornea depend on its hydration: changes in CH and CRF after excimer laser ablation qualitatively coincide with changes in RC, the correlation coefficient between RC and the initial value of CH is R= -0.619 (moderate negative correlation).
Conclusion: THz scanning is an effective non-contact technology for monitoring corneal hydration level. The mismatch of the hypoeffect of keratorefractive excimer laser intervention planned for patients with presbyopia with the actual outcome can be caused by individual decrease in the initial water content in the cornea. |
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1794 |
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Zhang, X.; Lita, A. E.; Smirnov, K.; Liu, H. L.; Zhu, D.; Verma, V. B.; Nam, S. W.; Schilling, A. |
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Title |
Strong suppression of the resistivity near the superconducting transition in narrow microbridges in external magnetic fields |
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Journal Article |
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Year |
2020 |
Publication |
Phys. Rev. B |
Abbreviated Journal |
Phys. Rev. B |
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101 |
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6 |
Pages |
060508 (1 to 6) |
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MoSi, WSi films |
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We have investigated a series of superconducting bridges based on homogeneous amorphous WSi and MoSi films, with bridge widths w ranging from 2 to 1000μm and film thicknesses d∼4−6 and 100 nm. Upon decreasing the bridge widths below the respective Pearl lengths, we observe in all cases distinct changes in the characteristics of the resistive transitions to superconductivity. For each of the films, the resistivity curves R(B,T) separate at a well-defined and field-dependent temperature T∗(B) with decreasing the temperature, resulting in a dramatic suppression of the resistivity and a sharpening of the transitions with decreasing bridge width w. The associated excess conductivity in all the bridges scales as 1/w, which may suggest either the presence of a highly conducting region that is dominating the electric transport, or a change in the vortex dynamics in narrow enough bridges. We argue that this effect can only be observed in materials with sufficiently weak vortex pinning. |
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1800 |
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Sidorova, M.; Semenov, A.; Hübers, H.-W.; Kuzmin, A.; Doerner, S.; Ilin, K.; Siegel, M.; Charaev, I.; Vodolazov, D. |
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Timing jitter in photon detection by straight superconducting nanowires: Effect of magnetic field and photon flux |
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2018 |
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Phys. Rev. B |
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Phys. Rev. B |
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98 |
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13 |
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134504 (1 to 14) |
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SNSPD, NbN namowires |
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We studied the effects of the external magnetic field and photon flux on timing jitter in photon detection by straight superconducting NbN nanowires. At two wavelengths 800 and 1560 nm, statistical distribution in the appearance times of photon counts exhibits Gaussian shape at small times and an exponential tail at large times. The characteristic exponential time is larger for photons with smaller energy and increases with external magnetic field while variations in the Gaussian part of the distribution are less pronounced. Increasing photon flux drives the nanowire from the discrete quantum detection regime to the uniform bolometric regime that averages out fluctuations of the total number of nonequilibrium electrons created by the photon and drastically reduces jitter. The difference between standard deviations of Gaussian parts of distributions for these two regimes provides the measure for the strength of electron-number fluctuations; it increases with the photon energy. We show that the two-dimensional hot-spot detection model explains qualitatively the effect of magnetic field. |
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1842 |
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Shcheslavskiy, V.; Morozov, P.; Divochiy, A.; Vakhtomin, Y.; Smirnov, K.; Becker, W. |
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Erratum: “Ultrafast time measurements by time-correlated single photon counting coupled with superconducting single photon detector” [Rev. Sci. Instrum. 87, 053117 (2016)] |
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Miscellaneous |
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2016 |
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Rev. Sci. Instrum. |
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Rev. Sci. Instrum. |
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87 |
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6 |
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069901 |
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SSPD, SNSPD, TCSPC, jitter |
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In the original paper1the Ref. 10 should be M. Sanzaro, N. Calandri, A. Ruggeri, C. Scarcella, G. Boso, M. Buttafava, and A. Tosi, Proc. SPIE9370, 93701T (2015). |
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Becker & Hickl GmbH, Nahmitzer Damm 30, Berlin 12277, Germany |
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0034-6748 |
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PMID:27370512 |
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1810 |
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Смирнов, А. В.; Карманцов, М. С.; Смирнов, К. В.; Вахтомин, Ю. Б.; Мастеров, Д. В.; Тархов, М. А.; Павлов, С. А.; Парафин, А. Е. |
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Терагерцовый отклик болометров на основе тонких пленок YBCO |
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2012 |
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ЖТФ |
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ЖТФ |
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82 |
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12 |
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108-111 |
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YBCO HEB NEP |
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Представлены первые результаты измерения болометрического отклика высокотемпературных сверхпроводниковых детекторов на основе тонких пленок YBCO на электромагнитное излучение с частотой 2.5 THz. Минимальное значение оптической мощности, эквивалентной шуму созданных детекторов, составило 3.5· 10-9 W/sqrt(Hz)sqrt. Обсуждена возможность дальнейшего увеличения чувствительности исследуемых детекторов. |
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