CINXE.COM

<!DOCTYPE html><html lang="en-US"><head><title>Just a moment...</title><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=Edge"><meta name="robots" content="noindex,nofollow"><meta name="viewport" content="width=device-width,initial-scale=1"><style>*{box-sizing:border-box;margin:0;padding:0}html{line-height:1.15;-webkit-text-size-adjust:100%;color:#313131;font-family:system-ui,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,Noto Sans,sans-serif,Apple Color Emoji,Segoe UI Emoji,Segoe UI Symbol,Noto Color Emoji}body{display:flex;flex-direction:column;height:100vh;min-height:100vh}.main-content{margin:8rem auto;max-width:60rem;padding-left:1.5rem}@media (width <= 720px){.main-content{margin-top:4rem}}.h2{font-size:1.5rem;font-weight:500;line-height:2.25rem}@media (width <= 720px){.h2{font-size:1.25rem;line-height:1.5rem}}#challenge-error-text{background-image:url(data:image/svg+xml;base64,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);background-repeat:no-repeat;background-size:contain;padding-left:34px}@media (prefers-color-scheme:dark){body{background-color:#222;color:#d9d9d9}}</style><meta http-equiv="refresh" content="390"></head><body class="no-js"><div class="main-wrapper" role="main"><div class="main-content"><noscript><div class="h2"><span id="challenge-error-text">Enable JavaScript and cookies to continue</span></div></noscript></div></div><script>(function(){window._cf_chl_opt={cvId: '3',cZone: "perec.columbia.edu",cType: 'managed',cRay: '92263fd97ba04c4d',cH: 'OrWp3UIB.3NTXHOZBT9LXn32ly3iRiCBJe91Dm9l95Y-1742316839-1.2.1.1-ThIinSi2oPowRgrM6FsCcwCPqLhpTnNp1zLJm5fTasEdx4NRX1.kXR3CnnEZjOeh',cUPMDTk: "\/membership?__cf_chl_tk=wyA2fUyEPI.HuxXOrnxgoxXhG.JPClxVYJ98W5rm0w8-1742316839-1.0.1.1-34Vl3VHWhnoy2Q5ZS3AhAHjuXwMdCpI1jatAHPgM1H8",cFPWv: 'g',cITimeS: '1742316839',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/membership?__cf_chl_f_tk=wyA2fUyEPI.HuxXOrnxgoxXhG.JPClxVYJ98W5rm0w8-1742316839-1.0.1.1-34Vl3VHWhnoy2Q5ZS3AhAHjuXwMdCpI1jatAHPgM1H8",md: "hjjyeBqOGClCDQ_.mVilc1Ad1c3KDy5k8YuVe0kIacc-1742316839-1.2.1.1-PPNmnbsOCQAPmQlusQOYwp3rCNxcYxP8IQJIF9M1LPs77cmcrs03hiBTcKtLgWEe4CZBOnKkJmVADiQ1e3fANHTLTBuYpOgb_J63okuYCOtEMXjLImQ6eyBsgDWKPYOishrVN4a30r0bw1JrgIvHAQ4X7vUK3LySAXWnXNNIiTktuHohNBv8vtQ1cXoMynXw9FFwunbXwiDQB38RyKqcZ04jjQ4NPOApV8TonDeWdlx0eMO9MtooFDglh72ZAQG7Wt.hgP.JfiI_fX18P6gsGPszumn5OgDrb7xx4inEI2trqMKJV73sHB7nFi1ZCBuXpMpPXv4IEPE_WmgfvgzmiSBRNJfc7DVXWA89zaWYm34kOHrhi9ofPDiU6i0EQ.U5BP7GMLStPncfGNTCYfXGqrJoL.A6r44.xbRbqDQO7KC6ZEOvcOTtdSlHNthYen4TscpATqDvnH9d5gP.9TORPw3KTT65_2ti9wB0mEZFPj7XQjtOirB.yM2c2NrPErRkUrTmR_lh9J2jreARVmeBFGBXpSfnD9hDcg2vBd6.jegrdHqbxCmmPFNOybuZ3ZlTx9dKUxp8JdJ3_nInez2lVufAhpFujNLUR3Aeb5pmBpWX8RdpV4XO_eUcj3mGxX8Cjm6kFDX.OP4kD6plMHECz6XohMT5EwEI1vcxR_XR1ba6YyZcnL8ht7YwpV3YybUjsXm3L.KoIhBf8rbklVB9Jz.c.oWQ.nOeEL_25pHwQQ_v_chAkc2rhhu9_kZ0jMkbLFem8tpYeY7h57hbvT_13ECRwpoxvKQMkW7JX9SzaxKNNZNq93ApJLVfk7BMiFuDBp1lUa.PXEzFynnaLprC177cuePXorQYDnlf285VgWqYybt16iEbHE9OHmY3sttmg1pEsoskSds4wTByXo4lxTTa5NlKkIOJLBJ.HF04fSguWSapDPctvNN0sByQ53BJLevlW137tknxYuOR_dhMZJl8FenByw38xO53igphEgLYwX4mUPewcnocSdbKz4PyafA6lcV30NSPn5m0KaYMUJoeF_Tw8JDUXNKLhQELoCMI7Da6DcX6SITJMrLq.mIItF2W61aoPOZgts90wf6Z0rP06tc24P9DpixxXLt5cXbj2WUNTOE6uGfvRYaV_w3985vBfELs72jVH9CS1fOkAYWodS5YAOaamgv3hq5QNehGU.Temez4PBUAFWoYMlHVS.6.n2yRSWouTf9zpJ20TvMYZPA7zKPKChqO91Twk1o",mdrd: "DMDIOsTA8LycFcMsz86ITXf7vyrStgBTzbd1VneuAko-1742316839-1.2.1.1-uMmP244D7x7M8HNMhl7uS0bTWoUo5p8c4ObFZf9dIVMTgBppz_J2vyKAbhD4tBYIs1QYKoWjrlVmhZ7vnSHuT1ctpSFO1aXpR3j0YAbRxodV9OsJAs5GD.yYGwQrXWv0bHPzQKf0DRDFooaVjjhHaus4Wf7QV_IKiOCbVapNGJGetzuX.yAVezvDszxz5HWM8.H3qxArkPlyPJ2_5pHHoU1_ApCoEAWqttc1266TCe2wiMKBUfRKCkq.jsQiffVRzaIZY4igUgSC9mRYIrcen9rtQZjBtuMkboSucM_JOm3ADsDR0SS32fV1ByPGAzGbmwRMimX4duImkTxXdqA.AvgpzRaZUBfPj7z7Da_p9LL_DUHFbfgFMvnBM8kfpIwwkbJbJSHVCiZZFTdZasUEwq9iV9t9gDZBYbxXDtgV9nTfW.59SkU7hSiGaLFV8JEG7.oQsMPIwmVK2yiu6BTildOKpSMc4ww9Qj0b8zjWd.qwraUmISxj2fH_IBgT1Domw6yig_PSWOLCZnm55iFGdETM1fECuMPs08Ln2dfxdsjRGjN3Xwnj9eRY82cQNN6NGwOQ1GVV_bfl2NDKWDrYLOd15KWSdbZHaRABS6hF3QRog7PjUiyiPCNnOreaLMq8TAzovDmri.fFQOS1BJjmrpebwTbQmYH.7ZsEV7GR1ivJIZfM20vTL.mWvFHuMB1TFKW1u7lszzem9kbcwQit6XvMobL5F6ihlnxf29pN6TKu5E7DoLo7BA04u0EG0RA0WFoay3fErktgppsngmCxqACEUDn8Ui7sRCIOOtewWUd.boPJ4mFyUunGiXD1c5pkrs1i2ta5BRqHURXcbp0cm2x.WKx3pcpql7x.iwADIKjj.eDnQYl1FgNlSM33q0980yUfY71Z4cTBxMR1TVGMbcMCCX7ECfKsJNO8qyO_rtcI94h0Qb3Y8MkQoT28bi2tZ4LO.NqdP1U39ie3uqzeySSxGYuxyidaw8v7KJzQUQwixCqF1RVkAVyDhPaHzn3Y57yA.FQqt4YViHKuanPHfB1pNp5VpUnFbzEYtFI.WzY_bHclJ1vhc_eT9G1JNLI50i.SG80GLFZ.EwnGGzqWKM_uQrks1gSs7XlyZKFO6koGElYw8rfIFQEIoWxuZQGHESK2zJNNDNOT3XVdP2K6bq.li2No9iZfI0xbO8G1lIx8.pRZCvNYGo.13OHUjl81T4Qf49ivgQH4WXZVG3sLmclhgtj8eYyDJ0XLYhPYHPCq_EpVG6Qw3RYpin4xDeN3cTAu8cuSJCyDwnGP8js9NoeOOhc4vd0ucwVjk18uyr2cE7ZX0k.ffSCkUY__JLyf0f4tFZu.qfFP509eYdXhXd_rHKcKcR5kWp9SSHo7ieHXmMl6EEgV3Z2ViGAjUVTRxBO0AWhTbkM2_IhSiiK022Aq8VnFNs9Ww.gdlFiDtQXAqYTk_YP8K0Eyebs7gGuMZpOXAdBn4tcXmB1rLbUfpz_Izlwg2ZvZkH.Pemk6Wx.Pt.qglkFHyr6D7e6TCiBxXvEy7vJAN_L8LkuE2U0K3JHlkebaquupO1.vHCve9uTrBkYBDsIsgKRu0uW5eIRhHyLe2PhCR5mBzL07xiy2J9nUesqixIkAdRvLgeaD9dpk9KoOFkheQcuJccDQIMSQ8hGGMFh1dYlg4EhDM9jcjgWq_DxIVweD4tNw2XgUw9DP3pq1ARGV3NkHaUdy_CVklT_O7wzqeHkdFsRuexyuZSB.ffvVX0OqBc3dxbnDMpnOU1i7SSGheA5ZD80h7nNWKZXVECI_0MGXX6h.507Um05AgMQ9YGe3O4dBZmvLST2BZZR0xexNlzwqG0sheHtCun2shSDVDBx0MvPRwc0vvGwlGsggppOKjwdV5a_YC9EZlPIJHgenmMVg.nFCu.NzgseZyuJ6zv1.mz0XQqbrABgN8oNOFjeQmNGWRapMNRWEIzReSuYX7vW6XdMUPJ3m6ZSjXaWLQnaLqHZqULDjgEU_fxoHcBSO_GZWc.OQSfJld5a_6_sv.zcN7H_wzfH4Ebw.Bs9FhAt37hGUJp8rgZCDrBTuM648wsHxWnnDkWA"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/g/orchestrate/chl_page/v1?ray=92263fd97ba04c4d';window._cf_chl_opt.cOgUHash = location.hash === '' && location.href.indexOf('#') !== -1 ? '#' : location.hash;window._cf_chl_opt.cOgUQuery = location.search === '' && location.href.slice(0, location.href.length - window._cf_chl_opt.cOgUHash.length).indexOf('?') !== -1 ? '?' : location.search;if (window.history && window.history.replaceState) {var ogU = location.pathname + window._cf_chl_opt.cOgUQuery + window._cf_chl_opt.cOgUHash;history.replaceState(null, null, "\/membership?__cf_chl_rt_tk=wyA2fUyEPI.HuxXOrnxgoxXhG.JPClxVYJ98W5rm0w8-1742316839-1.0.1.1-34Vl3VHWhnoy2Q5ZS3AhAHjuXwMdCpI1jatAHPgM1H8" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>