Diagrammatic Coupled Cluster Monte Carlo

We propose a modified coupled cluster Monte Carlo algorithm that stochastically samples connected terms within the truncated Baker--Campbell--Hausdorff expansion of the similarity transformed Hamiltonian by construction of coupled cluster diagrams on the fly. Our new approach -- diagCCMC -- allows propagation to be performed using only the connected components of the similarity-transformed Hamiltonian, greatly reducing the memory cost associated with the stochastic solution of the coupled cluster equations. We show that for perfectly local, noninteracting systems, diagCCMC is able to represent the coupled cluster wavefunction with a memory cost that scales linearly with system size. The favorable memory cost is observed with the only assumption of fixed stochastic granularity and is valid for arbitrary levels of coupled cluster theory. Significant reduction in memory cost is also shown to smoothly appear with dissociation of a finite chain of helium atoms. This approach is also shown not to break down in the presence of strong correlation through the example of a stretched nitrogen molecule. Our novel methodology moves the theoretical basis of coupled cluster Monte Carlo closer to deterministic approaches.Comment: 31 pages, 6 figure

Extreme Precipitation in the Eastern Canadian Arctic and Greenland: An Evaluation of Atmospheric Reanalyses

Extreme precipitation events are becoming more common in the Arctic as the climate warms, but characterizing these events is notoriously challenging. Atmospheric reanalyses have become popular tools for climate studies in data-sparse regions such as the Arctic. While modern reanalyses have been shown to perform reasonably well at reproducing Arctic climate, their ability to represent extreme precipitation events has not been investigated in depth. In this study, three of the most recent reanalyses, ERA-5, MERRA-2, and CFSR, are compared to surface precipitation observations in the Eastern Canadian Arctic and Greenland from 1980 to 2016 to assess how well they represent the most intense observed events. Overall, the reanalyses struggled to match observed accumulations from individual events (−0.11 ≤ r ≤ 0.47) but matched the observed seasonality of precipitation extremes. The region with the strongest match between observations and reanalyses was Southwest Greenland. Performance varies by event, and the best match between reanalyses and station observations may have a spatial/temporal offset (up to one grid cell or 1 day). The three products saw similar performance in general; however, ERA-5 tends to see slightly higher correlations and lower biases than MERRA-2 or CFSR. Considering the limitations of in situ observations, these results suggest that the reanalyses are capable of representing aggregate extreme precipitation (e.g., seasonal or annual time scales), but struggle to consistently match the timing and location of specific observed events

Diagrammatic Coupled Cluster Monte Carlo.

We propose a modified coupled cluster Monte Carlo algorithm that stochastically samples connected terms within the truncated Baker-Campbell-Hausdorff expansion of the similarity-transformed Hamiltonian by construction of coupled cluster diagrams on the fly. Our new approach-diagCCMC-allows propagation to be performed using only the connected components of the similarity-transformed Hamiltonian, greatly reducing the memory cost associated with the stochastic solution of the coupled cluster equations. We show that for perfectly local, noninteracting systems diagCCMC is able to represent the coupled cluster wavefunction with a memory cost that scales linearly with system size. The favorable memory cost is observed with the only assumption of fixed stochastic granularity and is valid for arbitrary levels of coupled cluster theory. Significant reduction in memory cost is also shown to smoothly appear with dissociation of a finite chain of helium atoms. This approach is also shown not to break down in the presence of strong correlation through the example of a stretched nitrogen molecule. Our novel methodology moves the theoretical basis of coupled cluster Monte Carlo closer to deterministic approaches.Sims Fun

Baseline characteristics and patient reported outcome data of patients prescribed etanercept: web-based and telephone evaluation

<p>Background: The anti-TNF inhibitor, etanercept is administered as a once or twice weekly subcutaneous injection for the treatment of rheumatoid arthritis, psoriasis, ankylosing spondylitis, psoriatic arthritis and juvenile idiopathic arthritis (JIA). Limited data from the patients' perspective are available on the use of biologics in the treatment of these chronic conditions and this evaluation was designed to collect data from patients who had been prescribed etanercept for the first time. This manuscript describes the self-reported baseline characteristics and health-related quality of life of patients prior to treatment. Follow-up data will be reported separately.</p> <p>Methods: Patients throughout the United Kingdom prescribed etanercept were invited to participate in an evaluation of their condition and treatment using a data collection tool consisting of a web-based system supplemented by telephone reporting (PROBE). Outcome measures reported at baseline included demographic data, the condition being treated, previous treatment with biologic agents and current and previous medications. Questions modified from standard, validated quality of life questionnaires such as EQ-5D were incorporated and patients made a global assessment of the severity of their own illness using the CGI-S scale.</p> <p>Results: A total of 344 patients/carers/parents participated in the evaluation at baseline, 290 (84%) by online questionnaire and 54 (16%) by telephone. Overall, the study population had a mean age of 53 years, was predominantly female (62%) and 20% had been previously treated with a biologic agent. A total of 191 (56%) patients were receiving treatment with etanercept for rheumatoid arthritis, 44 (13%) for psoriatic arthritis, 43 (13%) for ankylosing spondylitis, 35 (10%) for psoriasis, 9 (3%) for known juvenile idiopathic arthritis (JIA) and 22 (6%) for another condition/patient unsure/missing response. All patients were prescribed the 50 mg weekly dose of etanercept except for 1 patient with JIA (40 mg) dose and 2 patients with psoriasis (100 mg). Thirty-eight percent of patients with rheumatoid arthritis were not receiving treatment with methotrexate.</p> <p>Conclusions: The baseline characteristics and health-related quality of life of first time users of etanercept can be adequately described using self-reported patient data collected using an online questionnaire with a telephone option (PROBE).</p&gt

2002-2003 Third Annual Mozart Birthday Concert

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