Multi-level Dynamical Systems: Connecting the Ruelle Response Theory and the Mori-Zwanzig Approach

In this paper we consider the problem of deriving approximate autonomous dynamics for a number of variables of a dynamical system, which are weakly coupled to the remaining variables. In a previous paper we have used the Ruelle response theory on such a weakly coupled system to construct a surrogate dynamics, such that the expectation value of any observable agrees, up to second order in the coupling strength, to its expectation evaluated on the full dynamics. We show here that such surrogate dynamics agree up to second order to an expansion of the Mori-Zwanzig projected dynamics. This implies that the parametrizations of unresolved processes suited for prediction and for the representation of long term statistical properties are closely related, if one takes into account, in addition to the widely adopted stochastic forcing, the often neglected memory effects.Comment: 14 pages, 1 figur

Multi-proxy reconstruction of surface water pCO2 in the northern Arabian Sea since 29ka

We report here the results of a multi-proxy study to reconstruct surface water pCO2 concentrations in the northern Arabian Sea. Our results show that [delta]11B and Mg/Ca measurements of the planktonic foraminifer Globigerinoides sacculifer yield consistent pCO2 values with those reconstructed from the [delta]13C of alkenones when used in conjunction with foraminifera [delta]13C and Cd/Ca values. They reveal that this area of the oceans has been a constant source of CO2 to the atmosphere during the interval 5-29 ka, and that the intensity of this source was greatest between 11 and 17 ka, when atmospheric CO2 levels were rising rapidly. We interpret our data as reflecting variation in the strength of the Asian Summer Monsoon (ASM), thus indicating that the strength of the ASM varied in phase with summer insolation over the Tibetan plateau between 5 and 29 ka. In contrast to a previous study (Clemens and Prell, 2003), we observe no significant lag between the rise in insolation and the response of the ASM. Rather, our data support a recent study by Rohling et al. (2009) that northern hemisphere climatic forcing factors play a greater role in controlling the intensity of the ASM during times of intense monsoon activity, and that the southern hemisphere forcing is more important during times of weak monsoons

Urological leaks after pelvic exenterations comparing formation of colonic and ileal conduits.

Item does not contain fulltextBACKGROUND: The aim of this study was to assess possible risk factors for urinary leakage of a newly formed urinary conduit after a partial or total pelvic exenteration. METHODS: An analysis was conducted from prospectively collected data of patients who underwent a pelvic exenteration with conduit formation for advanced and recurrent pelvic cancer. RESULTS: Of 232 patients undergoing a pelvic exenteration, 74 (32%) had a conduit formed. Of these, 47 (64%) had an ileal conduit compared with 27 (36%) a colonic conduit. Twelve (16%) patients developed a leak, of which nine occurred within the first month. Factors associated with a conduit leak included involvement of R2 surgical margins (43%), the magnitude of the exenteration and a current cardiovascular medical history (27%). Leaks were not found to be associated with either radiotherapy or chemotherapy. The 30-day leak rate for ileal conduits was 17% (8/47) and 4% (1/27) for colonic conduits with enterocutaneous fistula only occurring in the ileal conduit group (2/47). Fistula, drained collections and sepsis occurred in 40% of ileal and 19% of colonic conduits (p < 0.01). Patients with a conduit leak had a longer length of stay (59 versus 23 days, p < 0.001). CONCLUSIONS: Urine leaks after conduit formation in association with exenterations are relatively common with a prolonged length of hospital stay. Positive surgical margins and exenterations involving all four quadrants of the pelvis were associated with higher leak rates. There was no evidence of a difference between ileal and colonic conduits and number of leaks. However colonic conduits had less total complications including sepsis, leak and pelvic collections with comparatively no complications of a small bowel fistula.1 april 201