A simple fluorescence lifetime imaging system using a gated micro-channel plate (MCP) image intensifier coupled to a CCD camera has been developed. Nanosecond-level time-resolved fluorescence images of a sample under a pulsed light excitation can be detected directly. With a rapid lifetime determination method for multigate detection, fluorescence lifetime imaging can be promptly performed. In the present system, laser excitation of sample and shutter action of an image intensifier are fully synchronized by means of an optical fiber delay line. In order to compensate for fluctuations in the excitation source, a simple intensity monitor circuit was developed. Details of the instrumental system and verification measurements on two component samples are presented.
Characteristic 4f photoluminescence of Eu3+ doped into ZnO was first observed on the red band luminescence. The intensity and fine structures of the Eu3+ luminescence and their temperature dependence are strongly influenced by the doping conditions. In particular, for the increase of the Eu3+ luminescence intensity Li codoping is not effective but stoichiometric control of Zn and O is essential. Moreover, the observed red band luminescence can be considered to be due to excess oxygen.
A new phase-resolved two-dimensional fluorescence measurement system using an image dissector tube (IDT) has been developed. The gain control characteristics of the blanking electrode (located between the aperture plate and the first dynode of the IDT) are utilized to allow heterodyne detection with low-voltage control signals. Heterodyning the modulated fluorescence and reference signals at the blanking electrode of the IDT provides high-frequency response up to 1 GHz, in contrast to the 20 MHz bandwidth of the dynode chain due to electron transit time spread. Significant improvement of time resolution is observed. Fluorescence intensity and lifetime data are derived from the dc and ac components of the phase-resolved signals, respectively. Two-dimensional measurements can be performed by electronically scanning images within the IDT. Details of the instrumental system and typical fluorescence lifetime distribution measurements are presented.
During discourse comprehension information from prior processing is integrated and appears to be immediately accessible. This was remarkably demonstrated by an N400 for “salted” and not “in love” in response to “The peanut was salted/in love”. Discourse overrule was induced by prior discourse featuring the peanut as an animate agent. Immediate discourse overrule requires a model that integrates information at two timescales. One is over the lifetime, and includes event knowledge and word semantics. The second is over the discourse in an event context. We propose a model where both are accounted for by temporal-to-spatial integration of experience into distributed spatial representations, providing immediate access to experience accumulated over different timescales. For lexical semantics this is modeled by a word embedding system trained by sequential exposure to the entire Wikipedia corpus. For discourse this is modeled by a recurrent reservoir network trained to generate a discourse vector for input sequences of words. The N400 is modeled as the difference between the instantaneous discourse vector and that word. We predict this model can account for semantic immediacy and discourse overrule. The model simulates lexical priming, discourse overrule in the peanut in love discourse, and demonstrates that an unexpected word elicits reduced N400 if it is generally related to the event described in prior discourse, and that this effect disappears when the discourse context is removed. This neurocomputational model is the first to simulate immediacy and overrule in discourse-modulated N400, and contributes to characterization of on-line integration processes in discourse.
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