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="120"></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: "publications.waset.org",cType: 'non-interactive',cRay: '91342383fe5bf8d0',cH: 'UWaVX2P0vQH1Vt6zCkejFpjBuBJGp7.BrOX.YS.Le1k-1739778125-1.2.1.1-_XmZ2EdaF3u48I5QF3x2NHBDTH6q9zHjvArZZEPuXAfIkBWmICMewNObWoJVF9Vm',cUPMDTk: "\/10013309\/harvard?__cf_chl_tk=eJZBUqX_3uR4GaftxxQaaz8t_Jp0VwoX0aM7hJHk3to-1739778125-1.0.1.1-pAwhpBxvIQAuvN20IKuuh5zjGNg9UGtl5LCi.MAqaBM",cFPWv: 'b',cITimeS: '1739778125',cTTimeMs: '1000',cMTimeMs: '120000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/10013309\/harvard?__cf_chl_f_tk=eJZBUqX_3uR4GaftxxQaaz8t_Jp0VwoX0aM7hJHk3to-1739778125-1.0.1.1-pAwhpBxvIQAuvN20IKuuh5zjGNg9UGtl5LCi.MAqaBM",md: "zILbzdiq0I0.MuS1c3WaXt_AVrK0_r3ugUV3Kd19gRc-1739778125-1.2.1.1-ii7H_EIf8pq7JGZZM2xmwqhgYpzs54QYsGWRYuzo3ftF4Zd_HR8xrHR1UjaZofKDJ4rHuTpKrgwJPu83P5hr7nrqFnJDHxpecJRpPr6Co0o4KbTfFHKiaz8Lx.irBkPd9VaUgkL1bpkJ8wGic0F0U6KZUfW5sWkjt2nYHCgDUbDhMcFFW3P4OYwNyTCwoe1LxRjRtuItXgggHwIg2pOmIdJ2STK5mjN1CJZOuNwJvr19GNziB4E2u2bIFIMPuzBu6TcKp4eBM5oGuP1L0Hn8LMg4ACRpDHeJXSKL52ywDdscMUyEBZDfycBp2SDNxOdIZ7VSht3y3TdR5VDaCzvhvpkjSfADtnFiqIVYZC0hmwZ5dJeEIw.b28N1chkiaHoaA6HhKV_7A.LBIRbAvyDcjX1.15NM4EJs9NaqhZWlETjuIEkMsHaByZb36ngV62JtV7.AVFEV2XFB97gmvVAWl6nDlyb_.vU1DzyO8VtGpX2prp48D5teGWQvapet1cQI9eIWDdungvTs1SrVAh7VucdIAonFihQtyYRhBD6X7Pfc_RuPo3JAaKyVgXQmMDAGNgfxOL_NOomA.0GGdHZq3qPQSeBstqtVCFQPXQ0sYRTq6j659aBZqL5TlEIqQ1Rbfyw9YCA_SJk69Tm6cWxPrDmhxPubCumoOyu6ovRr4J3zo39mp44rS33u4oeIwbvGa_eZYAA7Tq8f1LShJ5U6IOzp0ZcT4mQpNzMLwil5KlB_WGpD6RGsXuu.dE_9NVbAV5rbQRx7OhfqOaT79YVE_pvzrxIlNST7NKvRMn6JzwMABIfKLoIWUpKgXmWby3zxKcJJBVuRPThce.t0Td_LiQu.UgOCiDWSUAIpyF8HmSfm1cC9TYDEi9I8kuFds_G8Xn8IB_YCrEu4wtiuyzMLPHnuifVrt1kIVyq25qXoUy2eLHKDP02uTedkMPbwxy1CaW.bHwEnL.Gy6Gxf9pfFqZiWCv0yb4lHpTqOzAmUHxQabbT91qGypwKaQypiB553UR3ThYVK1bcvf4tMh8FWDAHWL16ASibnXunfRgbHiz9AMTrgVXvQ0E1TaU1r_a.imwHt23F_cCPVZEj81rNU_RUM4Ny14aGB3rUcuvDXt4Jsw_Dcw3PjJWmE1vESXWtYw5rALzfT6BFRnoMMLeOLsc67OPBhG.wqlZvoDP0wtPv2iP899mQVIc.v2eyRyOuVMR.3zG5h1ympjjv2ZHvUDadyMkmBGX5OB_f6GdfrqO.PsSvh7BDKbT1Y1mRHTjtFxPA1O0PmIQ0uKrDH.n_z5urel.eRzOKSnqDrZI6I7Lrl8Ej2OZlZIImQOuUQ3ys.c7xbniMGB8GEtPWb_MAC1l386CwuLeNH4IIiQPfHsK7oF6sbisS3I7Gf.7w05itaTphSihJFT6mwpjR_HmiIMMl6OLLKmEOoNc8c7kGcFe1i4S_n1fjQsUJ54emQSPl4LJLEPYjGn5hIynFeuGJW1jKxCE.MmzgyYjwy3SDjIv_vNj_SYqp_2_VoPXALENQyx2AC2DApHZosuQ5ck5l2Phibc2ewJ1lflyXUp9KRYBVPkghLU9zfBAaUMKX3Px35UoBhmzvsqXNKjkvtKufQBTfQed1eBTrk4VUotDJ6aU2eNXCrC6RuV2PPRalVtnfrxZVOWiQXIz7f3e3FGgnKIhdB1PMx_GRggmseaacKxJWJWRrnDQWYEUtCaJCAq9Fgu..krk4R6K7MawcLv0TFWXQSBsuOP9vSb.Iv9SmQSz4Li9LOfuFHPrAUcizDoMCJhRN0xgtYF3QQ3okGAbrw87cdSpmybP_SYwqBUe3e1KBJQJ_xBRchBaqWWdr5hD3Seg8YB887cD_d_j6I8i89xTZW1ZLbEgTA3M1ZJP754Nw",mdrd: "YJ7R9r0JOnjw9p_p.ub3WhLWTX9nWRosP8eJHKlYlFk-1739778125-1.2.1.1-zNPbkZxj6gw_aa7oYiGeOItaMn0GvItihVSd2F2Sf47LFPwdUFfwhzkseofjGS6F7Kw8aVEixwDkJb2V7bsztYGRpHNe7iB47.KxycM1ErtAvCwTrIwKUNUI7tccm3wi2qW5imx5jyqWhpvOSIPtSpRncVYL40YwhBY7VKZxVm4qK2RA6POcAJ2XEHoe_TLAsfoTTUSFA1SVUAeG2xq2GPLSiOiguOFLgkkmgMwKxfp30OY1vmqCAPPT8xYMbaxCo7HjwIG6pbHmYcsYBigOZuVGA6Wbs_ZLUtgQnpSWyostr_gmZinDF385.np.ewHoQPx3zvcMvH73juLOpgng7MtbPhjfwWP2.DxIaLJaoWO3Y8..hoHvMv6m7N3.iNkc8z8c3KY3VoYFDb0luEuHlls8klmEy1OfMhJPs9hJyhJzj2Oq7ws5tnx8UrKZ9ncAORz6brzFlYwhGXShMBKpzn0zBr9uqgs.mB_H0oBihg_IXHR5m01CT8gpMN8vtlWN9gnuKLgkyVVMKfVwj.l.46V5ak.XcLt0gg0p3MLYYZTUQFDva8R2YS7j6soCOglptW8Yoe8_ze88Za3xLTmBbfiW5.ZUkrImmQMzOCpPp3b0dZufGyZ4qUA6rSXdVFh1Fd57r6RaR08GW8otqxWz.8XEYsz1eIwassIG9DyTN3fNuNdvLeb0s6I62B7.1_KTHvlPCLu6smbqlmKgwiayy6UNX.F_tSi_W_nQiQ6zEBFIriHCmk63PrOiqcuf.ptBqa5MBWF1CurEibqrETlnqMGFTAa6UTo_9nj0cWBzDSmkAL_yrJ5xHKFMTla3Zx8sIoD2bPEhVEqJJuK04JD.qpw1Yp7YgbmEP7iicNXlxOUt1IXG5tFxkKdORxT85dUe8nWUr8IzZm2ioPRanbZOORTx3LISFXAkHqObuzlHgI3Btr.NjLvpnYZHlLpgrqM5WZ1vPCm5QZcplWUa7T0p4M7hwnkXzmd26H0Fg5ldl9d_StmXUxrD5go880nmBE0ng7MIwnEs1kj1t7ogjYzlONS.KGyEwusybGH9dQSuc2ELNg3xh4L4t6dA_CHDokeDyLbn08o_dp1aPEF7qWqpzhIHTCvEtN5vVqrrCC82VerosY4Iqu_oFEvCzVxKLIRPnKRgSpmI5XihhCyXev9eilebkSR_ybUpc1VBMQ3kbXFgFAVl.WLP_1hWLalvo0w2Kflnqa_J0xkQurzVvBsAwPWZpzIe_AkEwi1M3McQCBq5q1mJFbbUSBUAfEAOWE6V3HdgMf8UBwprCFfqtPuxBxAIx_DDwxLNSs2RGxCpx_E1qi.eT17lQd4hJIT8Ei99I7BAU2STQtHdvt24Klzg.QiZviVHRooJkKcP4QSaDPzpm2diCn6D.oIXQ_QjfqiVdWWT30B5EgHKx8UaV_NiBCXfpwuKf4sC0Q5xTGESH59g57TL6P80I_FN_ulwBpo7yFXZDRqjKePzvyVt73fqGdEt_j.J8yT.MUCiR2TLG1LJrKdomJn_hkee.uvW.Hmwbg7z42hp7ECsp0oIcbGdESA9TwuVRvqQyHoB5K4A1chbfXSEkpk531acl74rWmsCq3_FhtOMnb3R43PU.ZvwFfOH80Z0Ebb4j7rvmvZlKmL.U_qYSV2O.9qbaCe5tezhrwXYjGUCZ53XRQaQY7KYYD98lqFRt.Z6PCTKdJAFgkbi1Q62r8ssPaE43SZD5U2VQ0RP4KtyYXgGiRvGjiugSF8RTFyWat2IU93g1mkO2bkW4CPPMaGT3Wt70QIzQ.HuHsFy1dE_zjwQxe8UAtHdud_f8UCdO4wQQf4Y0WDUDc5AKcj3O6D86QPbK0erRZg.9d_5MgM1ebH.J8_PZlQqKI0ipV6c8dYjQgry1_W0JbOgDuPHpnIgNCp.pjlDRYj1_8Ztq3NFsTBM7yrI9IJW0dE20jOS7f84_CpV2t6f.AfRimMEPxFwA3Q8JzkmQxFl"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=91342383fe5bf8d0';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, "\/10013309\/harvard?__cf_chl_rt_tk=eJZBUqX_3uR4GaftxxQaaz8t_Jp0VwoX0aM7hJHk3to-1739778125-1.0.1.1-pAwhpBxvIQAuvN20IKuuh5zjGNg9UGtl5LCi.MAqaBM" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>