1 The influence of capsaicin-sensitive afferent neurones in modulating acid-secretory responses has been investigated in the continuously perfused stomach of the anaesthetized rat. 2 Ablation of primary afferent neurones, after systemic neonatal pretreatment with high doses of capsaicin, did not modify acid responses to direct stimuli of the oxyntic cell with histamine (5mg kg 1), pentagastrin (20 pg kg-1) or carbachol (4 pg kg-1).3 Acid responses to hypoglycaemia induced by insulin (0.3 iu kg-1) were not influenced by systemic capsaicin pretreatment or by acute coeliac ganglionectomy. Vagotomy abolished this secretory response. 4 The increase in acid output induced by gastric distension (20cmH2O) was abolished by systemic neonatal capsaicin pretreatment. Likewise, vagotomy and acute coeliac ganglionectomy eliminated this secretory response. 5 Acute intragastric infusion with high doses of capsaicin inhibited the acid responses to distension but failed to modify the increase in acid output induced by insulin. 6 Local application (7-14 days before) of capsaicin to the coeliac ganglion abolished the acid response to gastric distension. This lack of secretory response was not the result of a nonspecific destruction of the ganglion, since changes in intragastric pressure after electrical stimulation of the coeliac ganglion were unaffected by such treatment. 7 These observations indicate that peripheral capsaicin-sensitive sensory neurones, located both in the gastric mucosa and in the coeliac ganglion, play a physiological role in the acid secretory responses to gastric distension.

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The involvement of capsaicin-sensitive afferent neurons in modulating acid-secretory responses to peptone, a product of protein digestion, has been investigated in the continuously perfused stomach of the urethan-anesthetized rat. Systemic neonatal pretreatment with capsaicin, which destroys primary afferent neurons, does not modify basal levels of acid secretion. Acid responses to intragastric perfusion with isotonic (0.5, 1, and 2.4%) or hypertonic (10 and 20%) solutions of peptone were reduced in capsaicin-treated rats. Intragastric perfusion with hypertonic mannitol (18%) did not stimulate secretion of acid. Systemic capsaicin pretreatment did not modify acid responses to intraperitoneal histamine (5 mg/kg) or pentagastrin (100 micrograms/kg). Acute intragastric perfusion (10 min) with capsaicin (0.3 mg/ml), tetrodotoxin (150 ng/ml), or the combination of both neurotoxins reduced the acid responses to 1% peptone to levels not different from those of animals treated systemically with capsaicin. Bilateral vagotomy or acute celiac ganglionectomy also decreased acid responses to 1% peptone in control animals, without modifying the diminished responses to peptone in rats treated systemically with capsaicin. Gastric acid secretory responses in rats undergoing both vagotomy and celiac ganglionectomy were not lower than those obtained after each surgical procedure alone. These findings suggest that peptone stimulates acid secretion in the rat partially by activating a nervous reflex mediated by capsaicin-sensitive sensory afferent fibers. The reflex arc involves fibers that would terminate in the gastric mucosa and project to, or from, the central nervous system through the vagus and the celiac ganglion.

In order to reduce the response time when simulating large reactors in detail, a parallel version of the thermal-hydraulic subchannel code COBRA-TF (CTF) has been developed using the standard Message Passing Interface (MPI). The parallelization is oriented to reactor cells, so it is best suited for models consisting of many cells. The generation of the Jacobian matrix is parallelized, in such a way that each processor is in charge of generating the data associated with a subset of cells. Also, the solution of the linear system of equations is done in parallel, using the PETSc toolkit. With the goal of $ This work has been partially supported by the Universitat Politècnica de València under Projects COBRA PAR (PAID-05-11-2810) and OpenNUC (PAID-05-12), and by the Spanish Ministerio de Economa y Competitividad under Projects SLEPc-PFE (TIN2013-41049-P) and NUC-MULTPHYS (ENE2012-34585). The authors would like to acknowledge the technical support provided by CNAT and IBERDROLA GENERACIÓN S.A. for the realization of this work.* Corresponding author. creating a powerful tool to simulate the reactor core behavior during asymmetrical transients, the 3D neutron diffusion code PARCSv2.7 (PARCS) has been coupled with the parallel version of CTF (pCTF) using the Parallel Virtual Machine (PVM) technology. In order to validate the correctness of the parallel coupled code, a control rod drop transient has been simulated comparing the results with the real experimental measures acquired during an NPP real test.

Calculation of electron correlation energy in molecules involves a very important computational effort, even in the simplest cases. Nowadays, using the new parallel libraries (PETSc and SLEPc) and MPI, we can resolve this calculation faster and with very big molecules. This result is a very important advance in chemical computation.

Thanks to the advances in computer technology, it is feasible to obtain detailed reactor core descriptions for the safety analysis of Light Water Reactor (LWR), in order to represent realistically the fuel elements design, as is the case of 3D coupled simulations for local neutron kinetics and thermal-hydraulics. This scenario requires an efficient thermal-hydraulic code that can produce a response in a reasonable time for large-scale, detailed models. In two-fluid codes, such as the thermal-hydraulic subchannel code COBRA-TF, the time restriction is even more important, since the set of equations to be solved is more complex.We have developed an MPI parallel version of COBRA-TF, called pCTF. The parallel code is based on a cell-oriented domain decomposition approach, and performs well in models that consist of many cells. The Jacobian matrix is computed in parallel, being each processor in charge of calculating the coefficients related to a subset of the cells. Furthermore, the resulting system of linear equations is also solved in parallel, by exploiting solvers and preconditioners from PETSc. The goal of this study is to demonstrate the capability of the recently developed pCTF/PARCS coupled code to simulate large cores in a pin by pin level of detail in an acceptable computational time, using for this purpose two control rod drop operational transients that took place in the core of a three loop PWR nuclear reactor. As a result, the main safety parameters of the core hot channel have been calculated by the coupled code in a pin level of detail, obtaining best estimate results for this transient.

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