6,887 research outputs found

    Higher dimensional VSI spacetimes

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    We present the explicit metric forms for higher dimensional vanishing scalar invariant (VSI) Lorentzian spacetimes. We note that all of the VSI spacetimes belong to the higher dimensional Kundt class. We determine all of the VSI spacetimes which admit a covariantly constant null vector, and we note that in general in higher dimensions these spacetimes are of Ricci type III and Weyl type III. The Ricci type N subclass is related to the chiral null models and includes the relativistic gyratons and the higher dimensional pp-wave spacetimes. The spacetimes under investigation are of particular interest since they are solutions of supergravity or superstring theory.Comment: 14 pages, changes in second paragraph of the discussio

    Tunable subwavelength ultrasound focusing in mesoscale spherical lenses using liquid mixtures

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    [EN] In this work, we present a configurable spherical lens for underwater focusing applications, which consists on a hollow ABS container filled with a liquid mixture. Two miscible liquids with different sound speeds are required to implement this novel configurable lens. We show that by adjusting the mixing ratio between the volumes of both liquids, the sound speed of the liquid mixture can be accurately selected. This results in a modification of the acoustic jet properties and a continuous tuning on the lens focal length. This procedure can be fully automatized providing a dynamic control mechanism that can shift the lens focal length to any desired value inside a continuous range in both directions. Depending on the acoustic properties of the selected liquids, subwavelength resolution or even beyond the diffraction limit resolution can be achieved. We provide experimental measurements for ethanol-water mixtures achieving subwavelength resolution for a certain focal length ranging between 34.6 and 42.8 mm.This work has been supported by Spanish MINECO TEC2015-70939-R and MICINN RTI2018-100792-B-I00 projects. S.P.-L. acknowledges financial support from Universitat Politecnica de Valencia grant program PAID01-18. I.V.M. and O.V.M. acknowledge support from the Tomsk Polytechnic University Enhancement Program.P√©rez-L√≥pez, S.; Fuster, JM.; Minin, IV.; Minin, OV.; Candelas Valiente, P. (2019). Tunable subwavelength ultrasound focusing in mesoscale spherical lenses using liquid mixtures. Scientific Reports. 9:1-7. https://doi.org/10.1038/s41598-019-50019-0S179Lu, Y. F., Zhang, L., Song, W. D., Zheng, Y. W. & Luk‚Äôyanchuk, B. S. Laser writing of a subwavelength structure on silicon (100) surfaces with particle-enhanced optical irradiation. J. Exp. Theor. Phys. Lett. 72, 457‚Äď459, https://doi.org/10.1134/1.1339899 (2000).Chen, Z., Taflove, A. & Backman, V. Photonic nanojet enhancement of backscattering of light by nanoparticles: a potential novel visible-light ultramicroscopy technique. Opt. Express 12, 1214, https://doi.org/10.1364/OPEX.12.001214 (2004).Heifetz, A., Kong, S.-C., Sahakian, A. V., Taflove, A. & Backman, V. Photonic Nanojets. J. Comput. Theor. Nanosci. 6, 1979‚Äď1992, https://doi.org/10.1166/jctn.2009.1254 (2009).Thomas, D. C., Gee, K. L. & Turley, R. S. A balloon lens: Acoustic scattering from a penetrable sphere. Am. J. Phys. 77, 197‚Äď203, https://doi.org/10.1119/1.3041420 (2009).Parrales Borrero, M. A., P√©rez-Saborid, M. & Fern√°ndez Garc√≠a, J. M. Acoustic scattering from a spherical lens irradiated by a finite transducer: Focusing effect and refraction. Am. J. Phys. 79, 401‚Äď408, https://doi.org/10.1119/1.3546092 (2011).Minin, O. V. & Minin, I. V. Acoustojet: acoustic analogue of photonic jet phenomenon based on penetrable 3D particle. Opt. Quantum Electron. 49, 54, https://doi.org/10.1007/s11082-017-0893-y (2017).Lopes, J. H. et al. Focusing Acoustic Beams with a Ball-Shaped Lens beyond the Diffraction Limit. Phys. Rev. Appl. 8, 024013, https://doi.org/10.1103/PhysRevApplied.8.024013 (2017).Veira Canle, D. et al. Practical realization of a sub-l/2 acoustic jet. Sci. Reports 9, 5189, https://doi.org/10.1038/s41598-019-41335-6 (2019).Chen, J., Xiao, J., Lisevych, D., Shakouri, A. & Fan, Z. Deep-subwavelength control of acoustic waves in an ultra-compact metasurface lens. Nat. Commun. 9, 4920, https://doi.org/10.1038/s41467-018-07315-6 (2018).Assouar, B. et al. Acoustic metasurfaces. Nat. Rev. Mater. 3, 460‚Äď472, https://doi.org/10.1038/s41578-018-0061-4 (2018).Al Jahdali, R. & Wu, Y. High transmission acoustic focusing by impedance-matched acoustic meta-surfaces. Appl. Phys. Lett. 108, 031902, https://doi.org/10.1063/1.4939932 (2016).Jim√©nez-Gamb√≠n, S., Jim√©nez, N., Benlloch, J. M. & Camarena, F. Holograms to focus arbitrary ultrasonic fields through the skull. 1902.06716 (2019).Hyun, J. et al. Realization of an ultrathin acoustic lens for subwavelength focusing in the megasonic range. Sci. Reports 8, 9131, https://doi.org/10.1038/s41598-018-27312-5 (2018).Chen, J., Rao, J., Lisevych, D. & Fan, Z. Broadband ultrasonic focusing in water with an ultra-compact metasurface lens. Appl. Phys. Lett. 114, 104101, https://doi.org/10.1063/1.5090956 (2019).Chen, J., Sun, Z. & Fan, Z. Groove-structured meta-surface for patterned sub-diffraction sound focusing. Appl. Phys. Lett. 114, 254102, https://doi.org/10.1063/1.5096258 (2019).Oku, H., Hashimoto, K. & Ishikawa, M. Variable-focus lens with 1-kHz bandwidth. Opt. Express 12, 2138, https://doi.org/10.1364/OPEX.12.002138 (2004).Honma, M., Nose, T., Yanase, S., Yamaguchi, R. & Sato, S. Liquid-crystal variable-focus lenses with a spatially-distributed tilt angles. Opt. Express 17, 10998, https://doi.org/10.1364/OE.17.010998 (2009).Gorman, C. B., Biebuyck, H. A. & Whitesides, G. M. Control of the Shape of Liquid Lenses on a Modified Gold Surface Using an Applied Electrical Potential across a Self-Assembled Monolayer. Langmuir 11, 2242‚Äď2246, https://doi.org/10.1021/la00006a063 (1995).Berge, B. & Peseux, J. Variable focal lens controlled by an external voltage: An application of electrowetting. The Eur. Phys. J. E 3, 159‚Äď163, https://doi.org/10.1007/s101890070029 (2000).L√≥pez, C. A. & Hirsa, A. H. Fast focusing using a pinned-contact oscillating liquid lens. Nat. Photonics 2, 610‚Äď613, https://doi.org/10.1038/nphoton.2008.198 (2008)

    The High-Risk Plaque Initiative: Primary Prevention of Atherothrombotic Events in the Asymptomatic Population

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    The High-Risk Plaque (HRP) Initiative is a research and development effort to advance the understanding, recognition, and management of asymptomatic individuals at risk for a near-term atherothrombotic event such as myocardial infarction or stroke. Clinical studies using the newest technologies have been initiated, including the BioImage Study in which novel approaches are tested in a typical health plan population. Asymptomatic at-risk individuals were enrolled, including a survey-only group (n‚ÄČ=‚ÄČ865), a group undergoing traditional risk factor scoring (n‚ÄČ=‚ÄČ718), and a group in which all were assessed for both risk factors and subclinical atherosclerosis (n‚ÄČ=‚ÄČ6104). The latter two groups underwent baseline examination in a dedicated mobile facility equipped with advanced imaging tools suitable for noninvasive screening for subclinical atherosclerosis (coronary artery calcium by computed tomography [CT], carotid and aortic disease by ultrasound, and ankle-brachial index). Selected participants were offered advanced imaging (contrast-enhanced CT, magnetic resonance imaging, and positron emission tomography/CT). Plasma, PAXgene RNA, and DNA samples were obtained for biomarker discovery studies. All individuals will be followed until 600 major atherothrombotic events have occurred in those undergoing imaging

    Soluble CD40 ligand predicts ischemic stroke and myocardial infarction in patients with nonvalvular atrial fibrillation

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    OBJECTIVE - Atrial fibrillation (AF) is associated with a high incidence of vascular disease that may be related to a prothrombotic and inflammatory state. Soluble CD40 ligand (sCD40L), which stems essentially from platelet activation, possesses inflammatory and prothrombotic properties. The aim of the study was to assess whether sCD40L is a predictor of stroke or myocardial infarction (MI) in patients with nonvalvular AF. METHODS AND RESULTS - Plasma levels of sCD40L were measured in 231 patients (177 [77%] had permanent or persistent AF, and 54 [23%] had paroxysmal AF). Patients were followed for a mean period of 27.8¬Ī8.8 months, and cardiovascular events such as fatal and nonfatal stroke and MI were recorded. AF population was divided in 2 groups according to sCD40L level above or below the median (4.76 ng/mL). The 2 patients' groups had similar distribution of cardiovascular risk factors, age, gender, medications, or serum C-reactive protein levels. During the follow-up period, vascular events occurred in 6 (2 nonfatal MI and 4 nonfatal ischemic strokes) of 116 patients with low levels of sCD40L (5.1%) and in 29 (11 fatal and 3 nonfatal MI; 3 fatal and 12 nonfatal ischemic strokes) of 115 patients with high levels (25.2%) (log-rank test: P<0.001). Using the COX proportional Hazards model, patients with sCD40L above the median were 4.63 times more likely to experience a vascular event (95% C.I.: 1.92 to 11.20). CONCLUSIONS - This study shows that enhanced soluble CD40L level is a predictor of vascular events in patients with nonvalvular AF, thus suggesting that enhanced platelet activation may play a role in its clinical progression. ¬© 2007 American Heart Association, Inc

    Liquid-liquid core-shell configurable mesoscale spherical acoustic lens with subwavelength focusing

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    El copyright pertenece a JSAP.[EN] In this work, we present a lens based on a thin hollow ABS spherical container structure, which can be filled up with different compatible liquids. The acoustic jet can be dynamically shaped by either shifting the operating frequency or modifying the geometry of the lens. We show for the first time that a spherical Ethanol ABS core¬Ņshell acoustical lens immersed in water with low diameter-to-wavelength ratio equal to 6.67 and refraction index of 1.24 achieves a focusing spot narrower than 0.85¬Ņ. Experimental measurements validate simulation results and demonstrate the viability of these configurable spherical lenses in underwater acoustic focusing applications.This work has been supported by Spanish MINECO TEC2015-70939-R and MICINN RTI2018-100792-B-I00 projects. S.P.-L. acknowledges financial support from Universitat Polit√®cnica de Val√®ncia grant program PAID-01-18. I.V.M. and O.V.M. acknowledge the Tomsk Polytechnic University Competitiveness Enhancement Program.P√©rez-L√≥pez, S.; Candelas Valiente, P.; Fuster Escuder, JM.; Rubio Michavila, C.; Minin, OV.; Minin, IV. (2019). Liquid-liquid core-shell configurable mesoscale spherical acoustic lens with subwavelength focusing. Applied Physics Express. 12(8):087001-1-087001-5. https://doi.org/10.7567/1882-0786/ab2c7aS087001-1087001-5128Meng, Q., Zhang, X., Cheng, L., Cao, P., Li, Y., Zhang, H., & Wang, G. (2011). Deep subwavelength focusing of light by a trumpet hyperlens. Journal of Optics, 13(7), 075102. doi:10.1088/2040-8978/13/7/075102Papaioannou, M., Plum, E., Rogers, E. T., & Zheludev, N. I. (2017). All-optical dynamic focusing of light via coherent absorption in a plasmonic metasurface. Light: Science & Applications, 7(3), 17157-17157. doi:10.1038/lsa.2017.157Hristov, H. D., & Rodriguez, J. M. (2012). Design Equation for Multidielectric Fresnel Zone Plate Lens. IEEE Microwave and Wireless Components Letters, 22(11), 574-576. doi:10.1109/lmwc.2012.2224099Ding, T., Yi, J., Li, H., Zhang, H., & Burokur, S. N. (2017). 3D field-shaping lens using all-dielectric gradient refractive index materials. Scientific Reports, 7(1). doi:10.1038/s41598-017-00681-zJim√©nez, N., Romero-Garc√≠a, V., Pic√≥, R., Garcia-Raffi, L. M., & Staliunas, K. (2015). Nonlinear focusing of ultrasonic waves by an axisymmetric diffraction grating embedded in water. Applied Physics Letters, 107(20), 204103. doi:10.1063/1.4935917Hooke, R., Allestry, J., & Martyn, J. (1665). Micrographia, or, Some physiological descriptions of minute bodies made by magnifying glasses‚ÄĮ: with observations and inquiries thereupon /. doi:10.5962/bhl.title.105738Thomas, D. C., Gee, K. L., & Turley, R. S. (2009). A balloon lens: Acoustic scattering from a penetrable sphere. American Journal of Physics, 77(3), 197-203. doi:10.1119/1.3041420Knollman, G. C., Bellin, J. L. S., & Weaver, J. L. (1971). Variable‚ÄźFocus Liquid‚ÄźFilled Hydroacoustic Lens. The Journal of the Acoustical Society of America, 49(1B), 253-261. doi:10.1121/1.1912324Hasheminejad, S. M., & Azarpeyvand, M. (2004). Sound radiation from a liquid-filled underwater spherical acoustic lens with an internal eccentric baffled spherical piston. Ocean Engineering, 31(8-9), 1129-1146. doi:10.1016/j.oceaneng.2003.10.010Liu, T., Chen, F., Liang, S., Gao, H., & Zhu, J. (2019). Subwavelength Sound Focusing and Imaging Via Gradient Metasurface-Enabled Spoof Surface Acoustic Wave Modulation. Physical Review Applied, 11(3). doi:10.1103/physrevapplied.11.034061Ma, F., Chen, J., & Wu, J. H. (2019). Three-dimensional acoustic sub-diffraction focusing by coiled metamaterials with strong absorption. Journal of Materials Chemistry C, 7(17), 5131-5138. doi:10.1039/c9tc01243eRugar, D. (1984). Resolution beyond the diffraction limit in the acoustic microscope: A nonlinear effect. Journal of Applied Physics, 56(5), 1338-1346. doi:10.1063/1.334124De Rosny, J., & Fink, M. (2002). Overcoming the Diffraction Limit in Wave Physics Using a Time-Reversal Mirror and a Novel Acoustic Sink. Physical Review Letters, 89(12). doi:10.1103/physrevlett.89.124301Sarvazyan, A., Fillinger, L., & Gavrilov, L. R. (2010). Time-reversal acoustic focusing system as a virtual random phased array. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 57(4), 812-817. doi:10.1109/tuffc.2010.1486Heifetz, A., Kong, S.-C., Sahakian, A. V., Taflove, A., & Backman, V. (2009). Photonic Nanojets. Journal of Computational and Theoretical Nanoscience, 6(9), 1979-1992. doi:10.1166/jctn.2009.1254Luk‚Äôyanchuk, B. S., Paniagua-Dom√≠nguez, R., Minin, I., Minin, O., & Wang, Z. (2017). Refractive index less than two: photonic nanojets yesterday, today and tomorrow [Invited]. Optical Materials Express, 7(6), 1820. doi:10.1364/ome.7.001820Yue, L., Yan, B., Monks, J. N., Dhama, R., Wang, Z., Minin, O. V., & Minin, I. V. (2017). Intensity-Enhanced Apodization Effect on an Axially Illuminated Circular-Column Particle-Lens. Annalen der Physik, 530(2), 1700384. doi:10.1002/andp.201700384Yue, L., Minin, O. V., Wang, Z., Monks, J. N., Shalin, A. S., & Minin, I. V. (2018). Photonic hook: a new curved light beam. Optics Letters, 43(4), 771. doi:10.1364/ol.43.000771Minin, O. V., & Minin, I. V. (2017). Acoustojet: acoustic analogue of photonic jet phenomenon based on penetrable 3D particle. Optical and Quantum Electronics, 49(2). doi:10.1007/s11082-017-0893-yLopes, J. H., Andrade, M. A. B., Le√£o-Neto, J. P., Adamowski, J. C., Minin, I. V., & Silva, G. T. (2017). Focusing Acoustic Beams with a Ball-Shaped Lens beyond the Diffraction Limit. Physical Review Applied, 8(2). doi:10.1103/physrevapplied.8.024013Minin, I., & Minin, O. (2018). Mesoscale Acoustical Cylindrical Superlens. MATEC Web of Conferences, 155, 01029. doi:10.1051/matecconf/201815501029P√©rez-L√≥pez, S., Fuster, J. M., Candelas, P., Rubio, C., & Belmar, F. (2018). On the use of phase correction rings on Fresnel zone plates with ultrasound piston emitters. Applied Physics Letters, 112(26), 264102. doi:10.1063/1.5036712Liu, C.-Y. (2014). Photonic nanojet shaping of dielectric non-spherical microparticles. Physica E: Low-dimensional Systems and Nanostructures, 64, 23-28. doi:10.1016/j.physe.2014.06.026Li, D., Wang, X., Ling, J., & Yuan, H. (2018). Super-narrow focusing and ultra-long working distance by different shapes of dielectric microlenses. Optik, 160, 138-145. doi:10.1016/j.ijleo.2018.01.061Zhou, Y., Tang, Y., He, Y., Liu, X., & Hu, S. (2018). Effects of immersion depth on super-resolution properties of index-different microsphere-assisted nanoimaging. Applied Physics Express, 11(3), 032501. doi:10.7567/apex.11.03250

    Screen-printed Organic Electrochemical Transistors for the detection of ascorbic acid in food

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    [EN] Methods traditionally used for ascorbic acid (AA) detection in food are often expensive and complex, making them unsuitable for day-to-day determinations. In this work, we report on the use of all- PEDOT:PSS Organic Electrochemical Transistors (OECTs) for fast, simple and low-cost determination of AA in food. The performance of these OECTs was tested first with in lab-prepared solutions of AA with different concentrations. The effect of the geometry on the transistors performance for AA sensing was also investigated by comparing the response of two OECTs with different channel and gate areas ratio (g), in terms of current modulation, sensitivity, background signal and limit of detection (LOD). OECTs with smaller gate electrode than the channel (large g) show the best performance for AA sensing: these devices display smaller background signal, higher sensitivity, larger modulation and better LOD value (80.10^-6 M). Since the AA content in food rich in Vitamin C is in the mM range, these transistors can be considered sensitive enough for quantitatively monitoring AA in food. In order to demonstrate the reliability of the proposed sensors in real food samples, the response of these transistors was additionally measured in a commercial orange juice. The amount of AA obtained with the OECTs is in good agreement with that determined by HPLC and with values reported in the literature for orange juices. Furthermore, these OECTs can be considered promising candidates for the selective detection of AA in the presence of other interfering antioxidants.This work was supported by Spanish Government/FEDER funds (grant number MAT2015-64139-C4-3-R (MINECO/FEDER)) and Generalitat Valenciana funds (grant number AICO/2015/103).Contat-Rodrigo, L.; Pérez Fuster, C.; Lidon-Roger, JV.; Bonfiglio, A.; Garcia-Breijo, E. (2017). Screen-printed Organic Electrochemical Transistors for the detection of ascorbic acid in food. Organic Electronics. 45:89-96. https://doi.org/10.1016/j.orgel.2017.02.03789964

    Prevalence and sociodemographic determinants of public stigma towards people with HIV and its impact on HIV testing uptake: A cross-sectional study in 64 low- and middle-income countries

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    Background: HIV stigma and discrimination are drivers of adverse HIV outcomes because they deter individuals from engaging in the HIV care continuum. We estimate the prevalence of public stigma towards people with HIV, investigate individuals' sociodemographic determinants for reporting stigmatizing attitudes, and test the impact of HIV stigma on HIV testing uptake. Methods: This was an observational study based on an analysis of cross-sectional surveys from 64 low- and middle-income countries. We used nationally representative survey data for the population aged 15‚Äď49 years from 2015 to 2021, which was the latest available data. HIV public stigma was measured using an index of two questions about attitudes towards people with HIV. First, prevalence estimates of HIV stigma were calculated by country, across countries, and by sociodemographic characteristics. Second, country fixed-effects multivariable logistic regression models were fit to assess sociodemographic determinants of holding stigmatizing attitudes towards people with HIV. Additional logistic regression models assessed country-level income and HIV prevalence as determinants of stigma and assessed the role of HIV public stigma as a driver of testing uptake. Results: A total of 1 172 841 participants were included in the study. HIV stigma was prevalent in all countries, ranging from 12.87% in Rwanda to 90.58% in Samoa. There was an inverse dose‚Äďresponse association between HIV stigma and educational level, wealth quintile, and age group, whereby higher levels of each were associated with lower odds of holding stigmatized attitudes towards people with HIV. The odds of stigmatized attitudes were lower among men and individuals with adequate knowledge of HIV. HIV stigma was lower in countries with greater gross domestic product per capita and HIV prevalence. Holding stigmatized attitudes towards people with HIV was associated with lower testing uptake, including having ever tested or having tested in the last year. Conclusion: HIV stigma is present to a highly varying degree in all countries studied, so different approaches to reducing stigma towards people with HIV are required across settings. Action to eliminate HIV stigma is crucial if we are to progress towards ending HIV because holding stigmatized attitudes towards people with HIV was associated with reduced testin

    Food groups and risk of coronary heart disease, stroke and heart failure : a systematic review and dose-response meta-analysis of prospective studies

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    Background: Despite growing evidence for food-based dietary patterns' potential to reduce cardiovascular disease risk, knowledge about the amounts of food associated with the greatest change in risk of specific cardiovascular outcomes and about the quality of meta-evidence is limited. Therefore, the aim of this meta-analysis was to synthesize the knowledge about the relation between intake of 12 major food groups (whole grains, refined grains, vegetables, fruits, nuts, legumes, eggs, dairy, fish, red meat, processed meat, and sugar-sweetened beverages [SSB]) and the risk of coronary heart disease (CHD), stroke and heart failure (HF). Methods: We conducted a systematic search in PubMed and Embase up to March 2017 for prospective studies. Summary risk ratios (RRs) and 95% confidence intervals (95% CI) were estimated using a random effects model for highest versus lowest intake categories, as well as for linear and non-linear relationships. Results: Overall, 123 reports were included in the meta-analyses. An inverse association was present for whole grains (RRCHD: 0.95 (95% CI: 0.92-0.98), RRHF: 0.96 (0.95-0.97)), vegetables and fruits (RRCHD: 0.97 (0.96-0.99), and 0.94 (0.90-0.97); RRstroke: 0.92 (0.86-0.98), and 0.90 (0.84-0.97)), nuts (RRCHD: 0.67 (0.43-1.05)), and fish consumption (RRCHD: 0.88 (0.79-0.99), RRstroke: 0.86 (0.75-0.99), and RRHF: 0.80 (0.67-0.95)), while a positive association was present for egg (RRHF: 1.16 (1.03-1.31)), red meat (RRCHD: 1.15 (1.08-1.23), RRstroke: 1.12 (1.06-1.17), RRHF: 1.08 (1.02-1.14)), processed meat (RRCHD: 1.27 (1.09-1.49), RRstroke: 1.17 (1.02-1.34), RRHF: 1.12 (1.05-1.19)), and SSB consumption (RRCHD: 1.17 (1.11-1.23), RRstroke: 1.07 (1.02-1.12), RRHF: 1.08 (1.05-1.12)) in the linear dose-response meta-analysis. There were clear indications for non-linear dose-response relationships between whole grains, fruits, nuts, dairy, and red meat and CHD. Conclusion: An optimal intake of whole grains, vegetables, fruits, nuts, legumes, dairy, fish, red and processed meat, eggs and SSB showed an important lower risk of CHD, stroke, and HF
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