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: '917bb2668e67fce3',cH: 'UFdhrtZKBPn6yKmuz174OqPy33gcQt6ecBlAx6rTFGA-1740528466-1.2.1.1-ukichyVnTsJwB6FSKfASl5qKVUOtbUG3OtwExtN9h2dVpsbl41xEnEBfZ3PULgP8',cUPMDTk: "\/3783\/harvard?__cf_chl_tk=v1X1lv4XDbATmA887wdSOn0hL1kHdlQ1rvOMtYenYOE-1740528466-1.0.1.1-_2qZGLYKFYYfw8zXeQQbpcTocyhZs2PcpO0n7F3R8Mk",cFPWv: 'b',cITimeS: '1740528466',cTTimeMs: '1000',cMTimeMs: '120000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/3783\/harvard?__cf_chl_f_tk=v1X1lv4XDbATmA887wdSOn0hL1kHdlQ1rvOMtYenYOE-1740528466-1.0.1.1-_2qZGLYKFYYfw8zXeQQbpcTocyhZs2PcpO0n7F3R8Mk",md: "Qs2vnTeHIlW5RzsauChYHHmdhubTdN72Sr_YiBxp6Gk-1740528466-1.2.1.1-nnSMya79Ckc5GgiCuwMZL4MZaDgeaB5Sg1dt5o8.Ux1m0bXHC3asOny8JKRz7XO0cBDLFZMtWhNJsPZ1hPpBDJSerW848APrDdc7tWCFIKHQTE_XPTUDEskRXQ.J4mmCjcbVktigtmvkSf45D0pzUAZ.EH_G.MFvLp_PI79ABWY5RAwZY04uOeqD9z_8oVhmmvSsUpcuorOjB_a4840ODKJy8iHTMOECzRLMhB7TZeXcVVctNEBlpnc4UVtNq63OqZDP4PdrabZ7q77Od2CZGq4XC3q_Ymg5ixbabH8jS4GrKM_bf4Pi.jeaEMD0gGwoHtvbnF295jRhUI3aYkoRTOoo_L9AX4IAI0OUYviRTmu2H_IooqpM12ZA82HgmRXPwxTSLRXFZsxWpFVwFRRs4rluDeXznbEEgYGQ87QPjy5m29QhOmoW4wdGT1dpmO6IAsLful7hDr7Ub2MN5MQ6_JyNawT7IvI_79kWB49be1P.Tb4vDp4zSqyTv_VDmqU2.3L63YGnwRloRBKXifbWaVs5OfC1lcUzrRHFA9xIfm2AJmob0KaY9oz1pJjSQ_fzHXrYEUiuQznW.nksJjFM3HJ_irQ4qMcZX59GKdQU2vKRmCOEZh6wif6e8cO9rY3jrkpcqmZ5FoKCjRmlBoGZ4K4GavR7GyFhb696rbujKCIx1cBwURzf722epgOr6f.NS.JUtkxrdGWLmVZH3rA8SwFsDdtwXYRiEjTyLz6UTvZD2O5VhCEKX4BPWQL6yFWfBIxODJvVAhMp3vtlE7IQwrzivzb.vgxLRvQNJWqEb1qqFw0HVByjSDt8JJz9.hh7xiSSTcCm1Plb8yepvwtBEKddLoUy8IRiAxAiJvcKFcXNnjkwgYJ00RpqLXV6N86Bz4slSc66tb9YhPFr_Z.knt.pNbkjPUVG2lkjyDWKPimULoA.9KpwMB_WFIQHsvW7VcxdQmDrIdBeZn6MlLpbunKt3XZhqFYpRqtGrdBK0UCPxkKldLs9XnwGIJXQTvua3h30X4fbp0InsTNwn2myc38hYnuX4UFVc7Z7CHVA6qiInO11niz1KXBIaarTd6YuEOhE.Gubia6v9EnWhRWS2b08kRho32qHuTIP3GKSJmBbw3Lo6YF2Cf71UgdEI0Hkr1bUvJPuZTIgGrw.ap0vwW.y7tKpFWb7uO7eCA4IJa3Ur_3TL7fxL.1DnI15FtSwyyRXuSV7epjN5cslmsWGL72aOGSfqGZzSGjGAWp2pFQ7FR7jbXxAKoM4iviVKS.Sbd.1TAFb8afsjX3KGiH5MYddbbPOvhmCfg_RPrRZeJnTlVpknmg5k3xW2aZDonRiA1sZ7kPPR09uQOwurFMewKZxbJ7kaIXDln8g3j5puZwEImGhj2w35LUc4xMEXB6btPEUr5_BOXsqHEzkqIU3aOAgwD.zAmWGAXoAHn2fGnmKjgNjOtPLcrHjdbuJ4eyJHwTnZ8W1pu6QHWMUsOsy7LLzNcR7T5Cz5.GXKkLcAYOiFZrrb2Fod8T.kby3vCOKT.PcGaAVDwjKX2yqDkvBp.nfScsDq3qdzqXyqeNqko8iS25TSO2cIQhtaP187VmDG7R6bbViSrwVrIpflKg7U.hrzvLJVxiMoljJs3gEVx6PW8F8EpHPyqjzriOl7XXHg1ukktb06Wkwe9CoojHaPyBQMxyff0anpRfTMQ6OUBtpbnVs7RLEC0v_Wp3xRw_wK81VqGX8Vf.AKjHJ3maxX9N2OVGft7ivC8.iDW6v.wMJPxfo9EZeuy7Pd.MqzStVJdLEYsXhdonp6VlLVL6hsmtOVa7OBoHxFIuDLua7ot5CquH9nOqDCdlZblYAiHN6mpAq2P4RgsYKkZjCY40VAKO5Y1PNa3Mjuf7pACz9JzI",mdrd: "9ClACjRV_qtPhJZ4pE4_Rvf.HbaGN3EePXdK45Q1aqo-1740528466-1.2.1.1-DW76Jyy_5tgoqlL4U3_8SaLVv84EzeMMbSOEwomwVaCNypgkhR0Mfi2JVSeGNMW6dhC9Jyk1O_dgoWemgxbi_dYW_5I435w8LCUyQU4RuFr3O3.aynrqI_mH.o4yDDAad4xC3.LYfHBjhyMD93ETSgI1e8e3OfxEUrnZ7OBBJ0jpPpj59V4bdYJs6znUpseI8YcN8H6TVABnRQVAzwtXw5l2GxdrmGHmunC51tmtgrQqQdY.CX4P06zK8UN7CRHO2Hb4WftA6DhualEgcGbsicNP5FE.c7rEu75HhLcP06u3Z8URBkUjT._ccM1qBMxmLg6sNdqGqQWn.r2Tqo1SDE.03NcnbHf2fwwoEyKMUWljb5ukYTDSYXS9bX.hwlJlj4JuZKZlA9CwxbJUBhCll7B3WWRwvN7HDUPRSGD2sIyXeXSuJQgb1T_LMWaUgL_HRW2HhqjHi2t_NqV3RR_fj_b3TSuelVWGUDGqE4.1otrbtVG9CF68MQKQJiHb2wSb5O5bBAdXGF1gdgZCYggGHEZz.He5jsbb5JMnxaCY_4DjU7d5xzhvxNozrsNaDaDqWpagRpXDPBltI1LkLp2HkhpsXfhpFyS5x.lwZn3ACsNljLk_j2S8nuPzM8N2kMMP8YhFN7OrZ.tAei9ghbVoK_zuErT8hLF7aV8_Wwv9RM9Mr0Z1Egu0DGmacjeVKnNR2k1losclM3yruiufscvHhNpIHSTF3IgWZoz6WXk63opRbZ37wCZCqKr6INx_VCYCcC8Z2hIX_o52EuotJR5Mf7V9e3ct8WaOc9K3EUtdgBuH_rl8CRFZWHNK19rZjnC4ED4JtUpxh7UsyrLsspgATyZigxH7N7FoIiYX4QVfTPwngDevmXw.GTUJ.TiJhpUrV5_BqGylx66bWvNttklwnTkuyX0rG4teCJmceh3hXkwLwRFqBz1KQbcnGwymUHej2u0pH5dFU2CZmfEA7n6io7SUBRg2KDRPV2d1kjVgiyz_SezNibSbh6qpYTqZ.K6vqmtkXmp4YW1XS.eBxeMZNcgK3mcyIARv4vnZnBdZo1u1YVM5O2FjHIdoxnYA7eX.1DwtK_k2mxx8B2RPKphx3JrojioRCfR3E435PZNMifFWeMhQk22_5rm9te.uNPnDNBinRTs6ugyXNbDHzfN8nXeYOhfF_jFz_JwEduEaHtY1WuSP3mmpO5PuYg5arxSPYdfeAhEBEStjZzuwSGaDFnkkabXhUS6ngUnuQkWPFRgKnRMwCRoh2de0YlwwwoR0UuIOR2VpJEnMuznk7inOFAumtdL8jUCda9n0xtNEqCyR9UXhvaNGUMYzwp9n_YPlr3iN7TjaK2YbQSrmAgoekyFodAFLTxU7myfzZFh4qnEnYYt1MpBrg529BGS64Il2LQ.VAFUFCg1ICBn_yuVkTL20L6eWC8Wjrob6VU2cLa.3PY8UU1.mDfxhjwAF.vh64GMkRNYY7Lxky.grZwWkeyNc2Oq9ZF58k_Me1yYO0AwSnbnmO_cqYKvrUSkBkpw2YHU0snLpWVABDDzjPmP73b2UeIcc9fkT8WD7l_uAv.OtgNYrK3LC2Ytqw6_eYnKjpF5uEAX7E7fv8KZRQZIDJuEeUsiiiv8YY0L53i87XW8S2QcG2rVhvQUUaT9x.okLVtYEVDxSNdGgIGjK_B8keP..cX1u1iRxuV2trTe.LY69pvzRkVSAK7gARgKWZ0POdd3wWdCxDTwwXy9tZphcjVEEAco9Bh272ELlUQXH_Im__WP9Sr480WMGEQpKPj6eE4lCu3ltDv4qGhopZ0aatcbJtzOy3G6jkG0XGpRdBy1dR1zpINp2RV6VRnXNL.aAwCkaYV_.6vzL2LwPG8g725JvIHHR21P_0GOgGaGEsXdquAZLPHWF6g4LBrPFYY_Ux.rRJ7aYwwU1mD1af0QV2xGEwUNQJHBRPginSK8B7cNrwVwyLujWRZAt5U.uphioXP7Tc3ep0xGfvVKP1DaHgw"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=917bb2668e67fce3';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, "\/3783\/harvard?__cf_chl_rt_tk=v1X1lv4XDbATmA887wdSOn0hL1kHdlQ1rvOMtYenYOE-1740528466-1.0.1.1-_2qZGLYKFYYfw8zXeQQbpcTocyhZs2PcpO0n7F3R8Mk" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>