170 research outputs found

    Interaction of numerosity and time in prefrontal and parietal cortex

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    It has been proposed that numerical and temporal information are processed by partially overlapping magnitude systems. Interactions across different magnitude domains could occur both at the level of perception and decision-making. However, their neural correlates have been elusive. Here, using functional magnetic resonance imaging in humans, we show that the right intraparietal cortex (IPC) and inferior frontal gyrus (IFG) are jointly activated by duration and numerosity discrimination tasks, with a congruency effect in the right IFG. To determine whether the IPC and the IFG are involved in response conflict (or facilitation) or modulation of subjective passage of time by numerical information, we examined their functional roles using transcranial magnetic stimulation (TMS) and two different numerosity-time interaction tasks: duration discrimination and time reproduction tasks. Our results show that TMS of the right IFG impairs categorical duration discrimination, whereas that of the right IPC modulates the degree of influence of numerosity on time perception and impairs precise time estimation. These results indicate that the right IFG is specifically involved at the categorical decision stage, whereas bleeding of numerosity information on perception of time occurs within the IPC. Together, our findings suggest a two-stage model of numerosity-time interactions whereby the interaction at the perceptual level occurs within the parietal region and the interaction at categorical decisions takes place in the prefrontal cortex

    Effects of magnetic fields on the propagation of nuclear flames in magnetic white dwarfs

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    We investigate effects of the magnetic field on the propagation of laminar flames of nuclear reactions taking place in white dwarfs (WDs) with the mass close to the Chandrasekhar limit. We calculate the velocities of laminar flames parallel and perpendicular to uniform magnetic fields as eigenvalues of steady solutions for magnetic hydrodynamical equations. As a result, we find that even when the magnetic pressure does not dominate the entire pressure it is possible for the magnetic field to suppress the flame propagation through the thermal conduction. Above the critical magnetic field, the flame velocity decreases with increasing magnetic field strength as vB1v \sim B^{-1}. In media with densities of 10^{7}, 10^{8}, \,\mathrm{and}\,10^{9} \unit{g\,cm^{-3}}, the critical magnetic fields are orders of \sim 10^{10}, 10^{11}, \,\mathrm{and}\,10^{12} \unit{G}, respectively.Comment: 9 pages, 8 figures, 1 tables, to appear in Ap

    Numerical Analysis For Heat Driven Ejector Refrigeration Systems For Various Refrigerants

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    In this study, a numerical efficiency analysis for ejector refrigeration systems driven by low grade waste heat (65-85 °C) is performed. A 1-D numerical ejector model which was validated is applied to estimate the characteristics of the ejector. Investigation is focused on various refrigerants such as HFC (R134a, R245fa, R365mfc), HFO (R1234yf, R1234ze(E), R1233zd(E), R1336mzz(Z)), and natural refrigerants (NH3, R600, R600a), and their COPs (Coefficient of Performance) are compared. Main operating conditions (e.g. generation temperature, evaporation temperature, condensation temperature) are also considered to compare the system characteristics for each refrigerant. Simulations are performed for different operating conditions and their effects on system performance is analyzed. The results show that high NBP (Normal Boiling Point) refrigerants tend to show higher theoretical performance because of their high latent heat. In addition, it is found that sensitivity of generation temperature is less than evaporation temperature and condensation temperature

    Versatile and Enantioselective Preparation of Planar-Chiral Metallocene-Fused 4-Dialkylaminopyridines and Their Application in Asymmetric Organocatalysis

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    A series of ferrocene-fused planar-chiral N-tosyl-4-pyridones (S)-2b-d were prepared in enantiomerically pure forms. Starting with the chiral ferrocenyl acetals, 1-[(2S,4S)-4-methoxymethyl-1,3-dioxan-2-yl]-1',2',3',4',5'-R5-ferrocenes ((–)-3b, R = Me; (–)-3c, R = Ph; (–)-3d, R = Bn), N-tosylamino and formyl groups were introduced at the 1- and 2-positions of the ferrocene cores in (S)-11b-d with control of the planar chirality. After the reaction with ethynylmagnesium bromide, generated propargyl alcohol derivatives (S)-17 were treated with MnO2 and catalytic TBAI to give the planar-chiral pyridones by the iodide-catalyzed cyclization. This method is highly practical with a shorter and higher-yield sequence without using noble metal catalysts. Planar-chiral ferroco-pyridones (S)-2b-d were reacted with various Me3Si-NR'2 to give a library of ferrocene-fused 4-dialkylaminopyridines ((S)-1, DAAPs) in high yields as single-enantiomers by the detosylative amination. The cymantrene-fused DAAPs were also prepared in the same way. The library of the chiral DAAPs were examined in the two asymmetric reactions as organocatalysts, and some newly prepared Fc-DAAPs showed better enantioselectivity than the known species

    An External Beam Method for Multi-Elemental Analysis of Heavy Metals in Stream Water

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    An improvement has been made on a liquid target preparation for an external proton beam PIXE which is regarded as an excellent technique for multi-elemental analysis. A 2 MeV proton beam taken out to the atmosphere through an exit Kapton foil bombards an acidic solution target directly. Such direct bombardment enables the direct comparison of X-ray yields of a liquid sample with those of the standard solution so that one can determine the elemental concentration in a liquid sample more precisely and easily. An example is given for the analysis of heavy metals in stream water
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