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- 저자 : Haubrich, Christina (검색결과 3 건)
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ANALYSIS OF THE CONTRIBUTION OF STATIC VAR COMPENSATORS TO DAMPING OF POWER OSCILLATIONS
M.Nayebzadeh,H.-J.Haubrich 전력전자학회 1995 ICPE(ISPE)논문집 Vol.1995 No.10
Modern SVCs with additional damping loop have been applied to damp inter-area modes of oscillations. The damping feature of SVC depends on many factors among which placement and tuning are decisive This paper discusses the problem of locating and tuning of SVC in power systems with many electromechanical modes of oscillations. The influence of voltage controller and capacity of SVC on damping are shown. Included are time domain simulations to verify the results from modal analysis.
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Liu, Xiuyun,Donnelly, Joseph,Czosnyka, Marek,Aries, Marcel J. H.,Brady, Ken,Cardim, Danilo,Robba, Chiara,Cabeleira, Manuel,Kim, Dong-Joo,Haubrich, Christina,Hutchinson, Peter J.,Smielewski, Peter Public Library of Science 2017 PLoS medicine Vol.14 No.7
<▼1><P><B>Background</B></P><P>After traumatic brain injury (TBI), the ability of cerebral vessels to appropriately react to changes in arterial blood pressure (pressure reactivity) is impaired, leaving patients vulnerable to cerebral hypo- or hyperperfusion. Although, the traditional pressure reactivity index (PRx) has demonstrated that impaired pressure reactivity is associated with poor patient outcome, PRx is sometimes erratic and may not be reliable in various clinical circumstances. Here, we introduce a more robust transform-based wavelet pressure reactivity index (wPRx) and compare its performance with the widely used traditional PRx across 3 areas: its stability and reliability in time, its ability to give an optimal cerebral perfusion pressure (CPPopt) recommendation, and its relationship with patient outcome.</P><P><B>Methods and findings</B></P><P>Five hundred and fifteen patients with TBI admitted in Addenbrooke’s Hospital, United Kingdom (March 23rd, 2003 through December 9th, 2014), with continuous monitoring of arterial blood pressure (ABP) and intracranial pressure (ICP), were retrospectively analyzed to calculate the traditional PRx and a novel wavelet transform-based wPRx. wPRx was calculated by taking the cosine of the wavelet transform phase-shift between ABP and ICP. A time trend of CPPopt was calculated using an automated curve-fitting method that determined the cerebral perfusion pressure (CPP) at which the pressure reactivity (PRx or wPRx) was most efficient (CPPopt_PRx and CPPopt_wPRx, respectively).</P><P>There was a significantly positive relationship between PRx and wPRx (r = 0.73), and wavelet wPRx was more reliable in time (ratio of between-hour variance to total variance, wPRx 0.957 ± 0.0032 versus PRx and 0.949 ± 0.047 for PRx, <I>p</I> = 0.002). The 2-hour interval standard deviation of wPRx (0.19 ± 0.07) was smaller than that of PRx (0.30 ± 0.13, <I>p</I> < 0.001). wPRx performed better in distinguishing between mortality and survival (the area under the receiver operating characteristic [ROC] curve [AUROC] for wPRx was 0.73 versus 0.66 for PRx, <I>p</I> = 0.003). The mean difference between the patients’ CPP and their CPPopt was related to outcome for both calculation methods. There was a good relationship between the 2 CPPopts (r = 0.814, <I>p</I> < 0.001). CPPopt_wPRx was more stable than CPPopt_PRx (within patient standard deviation 7.05 ± 3.78 versus 8.45 ± 2.90; <I>p</I> < 0.001).</P><P>Key limitations include that this study is a retrospective analysis and only compared wPRx with PRx in the cohort of patients with TBI. Prior prospective validation is required to better assess clinical utility of this approach.</P><P><B>Conclusions</B></P><P>wPRx offers several advantages to the traditional PRx: it is more stable in time, it yields a more consistent CPPopt recommendation, and, importantly, it has a stronger relationship with patient outcome. The clinical utility of wPRx should be explored in prospective studies of critically injured neurological patients.</P></▼1><▼2><P>Using continuous monitoring data in traumatic brain inury patients, Xiuyun Liu and colleagues compare the performance of cerebrovascular pressure reactivity monitoring using wavelet analysis to the pressure reactivity index.</P></▼2><▼3><P><B>Author summary</B></P><P><B>Why was this study done?</B></P><P>The brain is vulnerable to damage from too little (ischemia) or too much (hyperemia) blood flow following traumatic brain injury (TBI).</P><P>A physiological mechanism called cerebral autoregulation (CA) exists to maintain stable blood flow even if cerebral perfusion pressure (CPP) is changing, and an assessment of CA as part of bedside neuro-monitoring of patients with TBI could facilitate individualized treatment.</P><P>A robust method for assessing CA in TBI is not yet available. The traditional measure used, the pressure reactivity index (PRx), provides inherently noisy estimates and
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