1,721,122 research outputs found
Deep learning the slow modes for rare events sampling
No full textThe development of enhanced sampling methods has greatly extended the scope of atomistic simulations, allowing longtime phenomena to be studied with accessible computational resources. Many such methods rely on the identification of an appropriate set of collective variables. These are meant to describe the system's modes that most slowly approach equilibrium under the action of the sampling algorithm. Once identified, the equilibration of these modes is accelerated by the enhanced sampling method of choice. An attractive way of determining the collective variables is to relate them to the eigenfunctions and eigenvalues of the transfer operator. Unfortunately, this requires knowing the long-term dynamics of the system beforehand, which is generally not available. However, we have recently shown that it is indeed possible to determine efficient collective variables starting from biased simulations. In this paper, we bring the power of machine learning and the efficiency of the recently developed on the fly probability-enhanced sampling method to bear on this approach. The result is a powerful and robust algorithm that, given an initial enhanced sampling simulation performed with trial collective variables or generalized ensembles, extracts transfer operator eigenfunctions using a neural network ansatz and then accelerates them to promote sampling of rare events. To illustrate the generality of this approach, we apply it to several systems, ranging from the conformational transition of a small molecule to the folding of aminiprotein and the study of materials crystallization
Diagnosis and treatment of pheochromocytoma
No full textEarly detection of a pheochromocytoma is necessary to avoid the cardiovascular complications of hypertension and to recognize the 10% of malignant neoplasms. Hypertensive changes, particularly hypertensive spikes and stable hypertension are the most common clinical features. A pheochromocytoma must be suspected in presence of various symptoms of which cephalea, tachycardia, diaphoresis are the most frequently encountered. Plasma catecholamines and 24-hours urine metabolites measurements have 60-100% and 72-99% sensitivity respectively. Radiologic procedures commonly used to locate a pheochromocytoma include CT and RM: they achieve 100% sensitivity for unilateral adrenal lesions and respectively 64% and 88% sensitivity for extraadrenal lesions. Scintigraphic localization with MIBG provides functional informations and is recommended for follow-up of the recurrent or metastatic pheochromocytoma. Preoperative medical treatment using alpha and β blocking agents or calcium channel blockers has contributed to reduce perioperative morbidity and mortality. Anterior transabdominal approach is advocated as the standard operative procedure; this approach allows ready access to any site where tumors are obviously present and permits thorough exploration of the abdominal cavity for additional contralateral adrenal or extraadrenal lesions. An accurate preoperative localization of a sporadic, unilateral, of less than 7-10 cm, benign neoplasm constitutes the indication for the laparoscopic adrenalectomy. Pheochromocytoma-free survival were 92% and 80% at 5 and 10 years respectively; in living patients without recurrence, hypertension-free survival was 74% and 45% at 5 and 10 years respectively. Extraadrenal pheochromocytomas are frequently malignant (36%) and are associated with a high incidence of persistent or recurrent disease (32%)
VARIAZIONI DI ALCUNI PARAMETRI BIOCHIMICO-CLINICI IN SCROFE LATTANTI IN RAPPORTO ALLO STATO DI NUTRIZIONE PRE-PARTO
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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