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: "dl.acm.org",cType: 'managed',cRay: '8e75bfd71cd48950',cH: 't7COBlm6e3hUANHLaMbZ6_SSoV6G9.RQ2v95SNUo.9k-1732413039-1.2.1.1-rtDuA7_QRz95Lcbv3bG5cMe36gjBbS8u2ovtwevh_AwY9sOxxjXMDLr_vY5hLT1k',cUPMDTk: "\/doi\/10.1145\/1236457.1236460?__cf_chl_tk=CgAWAVi_y9xGEyv5lP0D6OIpUvh3gr9Ibuk528kMHTI-1732413039-1.0.1.1-gIxxwxxni41jiM3lS65ej9TtH4KSHte43tEGo5LBzm4",cFPWv: 'g',cITimeS: '1732413039',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/doi\/10.1145\/1236457.1236460?__cf_chl_f_tk=CgAWAVi_y9xGEyv5lP0D6OIpUvh3gr9Ibuk528kMHTI-1732413039-1.0.1.1-gIxxwxxni41jiM3lS65ej9TtH4KSHte43tEGo5LBzm4",md: "2Pn.pCRYnXR9VrFpM_9vnBTcN920a6Ju9nVCmKd5w2I-1732413039-1.2.1.1-27pBQrAV.EFZ1r7hEnyL7M8AznnLiZ6VSWMokmCDOsutSvQ9XrpoiCR_YuDiDoOm58AQPhCgXAYkxQKQIVJJ1Cat0_uSHEietP4vRQymIF6Ugl8ZTG.eAICc5iP7A2gTrP3PVTbnnuVzuVgi1oIqUSPCGfebu0mDeCz77iE0dHxUwMeAA1WF7w0c379tB54IPfNovXK2upct.uU77TGS9QxRJC0SYmulX6uAaDLt3O409F.4g04Cn6Ptob0Kcv1nuQZZcH7YgT85obDXEnKxCIsjh37c91iAnNGWwbn1y92aThjITylymXcGABFRTNE6.Q_ozcNIF2lLw4YSTbYB9k4HEC8RClALluZq2Dh1uZQKe_6A5tOO_O.QnyRoyc5WfIdjENApS.4ZDvZANmJv0JxXif4FuI9rKODSViHEeJi9b8B.XNkHQPri7VKjHzQTgUSXzaePLZN5XqdzRSlsw60g4AQAm8X9U1YWDgZNecbTdmfYdTEW2SQXjkEsWoUFNtCcnbhbkBgE0HVGMFTq1UHx_n.pUJQX.oFe3HLvoIGF4qJVsdDg8_vEV1hpOr.dHPd2tspbNgl0p48dcHwOFtxiuiT9OPXMImgqwe3xkDfOLBFvx4du8w3VgAJHJLtg8sTi.heMMWFmCzY8NoXd2DK2m.2NtSpu9gjq.UQDxJ91MIgF7DweWYN9yL2marlS2fnAJf25UFzted5i2a08eRxM9mwWEiFoxEC_lRLZ6mlvTtRV_sBHUhSsZ9cuTLKXfCG31sWftgGO7hMNQxRQ_8Mi_MtV6iMDml96fuJa_cfTKVEgF9PntXbLOBOirb4l.pm8ScGiQzcSAgRMGvoaPaCVEJaFwBoFaqO0dfU9jkvFywe3L.FEZQjVd3UDuAkpDlrwCBx2T_dvK4TKakMir_pTEMiZPYJbu.pRxd2yoVcKkvUgIc5mtti30ortjVvPQbTPl3Lwd1cPa1l7ZW_YxPUrrA6XhsB5l6Tu85Jiq5UTKCNMqTaoJ1q9qCk1CLQWl0kSSOWoBR.KbnTq7.ErCCHcoLRSKo5PZjdWbTzCfT0YnjCpJkLm2cMXfGboXojQGeHXkXlbgL4Yg51FLoQXap83PUfpp_vCKHXxyjFSGzO9kMt62pRKz9Q1XKPBqln2h7e53reIvESTaP8OqTijQLVkEFTPRRDaSur49QQdA1_lnFpdYgpTzYAfiv9hNYyXLYt_rbKsVY3Lzacr1MrhTcJBQxLOMYpMfInx_Dxh.iyl1URqW5beDG0IHd_BU6F6P45Uk0s4sccTok8aSEJdEi_vJYRTcDzbaCs098YTzRGQ.oLq5eWOCJpI3gAwNpeiX_9hq9pnLlhoieMOBV84YKBlSv0tF_EyUYqF6HebpG_6pVMRQY_4.hve4LJXl7FtFm9nfviT794pFtidrQiYNEj_TV5dymQZ3xdHMcrTU_Eunzlw9scr1W54hatCmI3ZNn2anj.y0hVWNeXg_F2xal7rPSEnuxf2Iuti883gA3eDi5ow1PRm2Xog.mz3a2mtDiGL4mHEpo.yQiGQpIb88cbibBL8kGI2nWaONCYsH8V.qBnrVFJ9U.Lgo4jYDYEVKcIdqeCxGJNmYqLP1rvZkwAD4nSn1MWHNuWMHwCTlvOBIhuM3EFN6NEnOM5HrK_oS0NUoQCmkfp2o.G3y8qLPQ40s9DXenUL8xZgH3Aasj3UBYvprVYRt1P8o1UE44sEZXKU1e6fehqpA2Y97j65MsrRGuc_gyVUER8BSPg75kobUa1cYOgwTnqNh4ch1EIQDfBb4NLlJXAkjTgvZ0YRgG5z6k6NEke4FreRXEswIGq4UxD53G.Q8tJxQbRPrkIY1dhD8rzFY5yamTWBUwcICUUh6cCgQoU6aHq3ULDIusm6dImT67hQ424bIbJIMMg0EPGP3_4RAYukrqGn2PlPafyX9c_Mkg3MgRAPo67xwEYpWsRYcuA9NHy1UQjeZAuJLsB.hB4AxcqsonxA3sLud4NucroeJCOWjfj3P8pcExNIUMxju2XEDw1ng6_eg9trYasen0f7jH2DCdelbo.cxBseWLxeRvC9H_0v77t857r4f3LK6GohpClcge581IgIvHHhPl8NU.b1jFrgURDO5xLmsJtPe8fDrMhbJHq1lETYoctQ2qhyj8TPpCM0AH1gEisz3OTFAFUo_2z3GuKnT05IacsFVd227XQFXlSuhnO6Nppx8NeWqTIHIScjg6_9xQIgdqZ_gNkm0iiSSXiKPljMocfbksHBynLcXoHg.qWmLtH1Hr4ERGrFARrHM8j2qu0cMfONYa59eAzuDy90i2fBqcw4WKL_Fy18_6xnR.3rga_1VaN4r3ehvZPyYidS1AKSKNpYcwqXRcJHuTlX0hdPMhrnfxlOizulmhsTT7MTmvnKol7EuAT8LFHi83vOyOR.0swsFwC4HcIqxoG6jBbMEHEqT7mVAV8XcylR70XEAZ418Chn9DVGIr8YHTTB4ILrqFOm5QjZNoxWJGK5s.ZTUumC2a69iZkTZvj7vbYQx_KAv9mkMKs0NCHSr6FPj4uNuEiLKeTBz78uEHKDBVcNAAS_96eTKF1aVcdR_ihZTB9byp.epJoFDnEJH3YLjjpEOh6QuaLqchOQWkBQ51Ghgp1b22.G6EopNsCgUzKphU93UkkwSjKEDmxiV.FLEaECYBlOgXVdRxw0rBWktYTMUKSoC.ukPnDZB3zmnK5lS2uO.WJWEIXYAJgTCbUwInFso6Qy_HrmQzz4ijRp4kKdyqPLOBxIXCVhJ1mv12ZWVhj9uR0aOqwVfZyE77qZwlI.WxJghG_.prOtB0tOXAVeoUC1mcsMS7YvW4VfInbaC.gUj4ETBNCC0U2As1SawQJ_3oZ1AWMXjkUXJfy_Am.nLLkmE76dCSV3GTYyFc3MdTg.Nna6jF97DQxMkBUknY5un6VqpRzpgXOBiqsM2B7prkiIxQzuJ0SElr.bViI7oHMYk.8zAfoOT9AxDkb9",mdrd: "ZWiW4E5G.NUjfV4hKQ2X.sIhzvrbolwTIYjkyaT1ypE-1732413039-1.2.1.1-HRXU6KFe39GEDHkRz.wL1Kr7MIqJGWwmcmC2i0LVs6.MFPURnMYp3bL_PcuJ9TtGL532Hc6NCQbIcQMBupqgPrwnIo1RUd94f9HPFxsh83_UHk7nlnLc7P8WE8Pn_tRWKSrJwx7ozx97D5DL3VPKlapx2mF6ea8vhN8hqCJi33yJauM.6uqjbB7LSHhMlxqftF740fc87pBrGmDFEoHCxy8BL5vWCPpSAzXyTcPK7dr_5Vt.m3guKZRkNoMELcpDaSnswSvDfEOWmsoMA3XFbqb1zTeJyHPAEiM7v5ZO17m4NwrY.zfExUozAoWdoP8k4FSkixZbbEkPHTmgy6oobuMBHdYJM.BFqxn4DCTcCACGN8VVhnKoiQa6L7rHhq1UCxLOGhnJ7IyUQn1xzShxMPZo42KUcVZhsRZZr8pet37OZjF3txYj5652KdjOmSrWga_KEi_fzEeVQgtjwilEy7EZ_AgiucOVxy1.WGqoUUtrY0ZqEKn7c61VYpJICalFowWT4FYfH1CljL6s7hffs3kDtm72WRtBruwZwmpC8FqiY5r0VPFsIBXTBnXv2w1O0K2uHsI9E_R.ey00mQXauldJTP4ClmNp7cR4F1tLkG3s02iDA1IocyBKxVe3Q1MOWCVVEgxvZ6o02mdWYKda.4e3NmZDntStXCk_QyMAAuAdpGszUj53OIeC6L4AlPipox5rnFEbWahbLJOJ474tLjS_EA7Z5OQpFPqstyYmhfww.9aQuUu.2FD7LCtuyoMg.F6hRkn1RIOOE1ZgoiwSeXVSFz2Ou8GAMNguccJMdf_lpHARnecQJWcDmWgJa8Ja3VoAaPUNaMbjO_f4jL587rW0vCW0VY.8t7RusDmR24..sX8EuL.ckxKjN1v0cHAgZZJ3QzxE43sIIpiFtEg27LR.8ofaWSP0rS1I.3RqIeV3yXfPonExZ1RMbZK4Dg1nOyxKLQ0gBiN8Cw7M75PApdcwV5KdXYx9LRUZfC28_b_ouTFdDVMF8vu7dsyIFEn8OspWVMOxRatvHRqNdSA7tgZ80Ir7SmVTENTIoCYHnZxm1FhRaUtZJsxooa9DcAHSvWiA8JogoKNk_6.Xgh8DMK5pYlzKsxaN04uBCXsM8jy4jXE3b1mXS3qyw9YUUsS0Suy8Ge1JOCcb8VybdodnUdp6ujZD7jO8RR6gKWcPEuus75Gxb7LfYFaR8cUXvbI5g6UHLqex5M_cvfI3glQhBiBDLUUYp3LOvYgUpwrKJJAHFuXONC4wj6gMWBhOlJagvNmXUuWnd2CNgJyAl02m8nUaxMNZ2SHAi_hL8Z83SLW4qiJW2xIixY0mGGDOwf1QK_1IUbm.tY_NwzOU77asUJFy5QGxlVSwsTZNQqa6V8xSNhBFVgQeXAZbkufzeAYUjXcjNAYYS0HIGb7SFCub_57x7GZUoQrhun_RFrHdjwMwcei4uKGni91RUtnzAVjNXyyorMe_N9PHgYWIdZvP0LCyhOchB56IND6KVnG0VYm6nhNdlZfEeJKetCWxcPWIreAkU4haspZVTY260YcRGP3X5CP5IO3oZry9siaGMZBsaTaBlx0mhvf_TPMyJK7bfNPEdnRKlSxKOz1PpR.TJpLicPn1uA0YpfANvD_ofbK2Cc8SddEk.z1ZlAtX3Ffm3QFoRnVC.lzFA6bzXXklZNea8kOBd7QTaaCDjVgd4puf6YY4IcHjdqihNfHK_FwfQHtXwVLForMdp1NogXkyuB6iJulc188ISiC3hDf0UQea23xc8F5d.rJGgzkUV15UjBX05VnZ6KtyN45Si5.2Y7uozVQ1bTqq6b2tzoAMqVzk0A1FPUXU_adcQPvIfB68xM56h6BQ5WBF9UYMWmHpcPiFmGOcHJqkWbAm8CmD01Uoo0sESV9gZG2zAKl9UcbHIKAJ7y53rv5GwKsNi2weAJj7_LHXHgbbVGI_zgRHWdr6.VjZGrlohco1hwotbKCF"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/g/orchestrate/chl_page/v1?ray=8e75bfd71cd48950';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, "\/doi\/10.1145\/1236457.1236460?__cf_chl_rt_tk=CgAWAVi_y9xGEyv5lP0D6OIpUvh3gr9Ibuk528kMHTI-1732413039-1.0.1.1-gIxxwxxni41jiM3lS65ej9TtH4KSHte43tEGo5LBzm4" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>