Modeling the Contributions of the Exocytotic Machinery and Receptor Desensitization to Short- and Long-Term Plasticity of Synapses Between Neocortical Pyramidal Neurons

Short-term synaptic depression (STD) refers to the progressive decrease in synaptic efficacy during a spike train. This decrease may be explained in terms of presynaptic and postsynaptic processes, such as a decrease in the probability of transmitter release, and postsynaptic receptor desensitization. STD may be very strong, and is release-dependent in neocortical pyramid-pyramid synapses. Using a stochastic synapse model, we suggest that the main source of depression in these synapses is the step of vesicle priming, while vesicle depletion and postsynaptic receptor desensitization are proposed to play a lesser role. Our results suggest that vesicle priming may explain not only the release-dependent nature of STD, but also the observation that an average of about one vesicle per active zone is released in central synapses, without positing forced univesicular release. We propose that the latter phenomenon is due to a low priming probability. Our results also explain the effect of paired pre- and postsynaptic activity on STD. In neocortical pyramid-pyramid synapses pairing induces a form of long-term potentiation that has been described as a redistribution of synaptic efficacy (RSE). We propose that RSE is due to a pairing-induced increase in the probability that a primed vesicle will undergo release in response to a presynaptic action potential. This increase may be due to an increased Ca^2+ influx through voltage-gated Ca^2+ channels, or to an increased sensitivity of primed vesicles to this influx. The results were obtained by constraining the model with experimentally observed levels of release probability and other synaptic variables.Defense Advanced Research Projects Agency and the Office of Naval Research (N00014-95-l-0409); Office of Naval Research (N00014-95-l-0657)

Deprem kestirimi için web tabanlı çoklu bilgi iletişim sistemi

Bu çalışmada deprem algılayıcıdan elde edilen verilerin yanı sıra deprem olayı ile ilgisi olduğu düşünülen diğer fiziksel büyüklüklere ilişkin bilgilerin internet ağı üzerinden sayısal olarak aynı anda gönderilmesi incelenmiş ve pratik olarak denenmiştir.Denenen bu yöntem iyi bir sonuç vermiş olup elde edilen verilerin gelecekteki çalışmalar için umut verici olduğu gözlemlenmiştir

Managing Knowledge for Innovation and Intra Networking: A Case Study

AbstractRecently, innovation has become a very important issue, as it provides a strategic advantage for organizations to outperform competition and remain agile in the market. Additionally, knowledge management is considered to be a strong support for innovation. Managing knowledge for innovation is a difficult issue for organizations, because innovative knowledge is implicit and hard to capture from minds. To make this knowledge explicit, we must use supportive technologies. In this article, we focus o n intra networking - a type of social networking as a tool for managing knowledge for innovation in organizations. Intra networking is known as intranet in business and technological society. We define intranet as an internal or private network of an organi zation based on Internet technology (such as hypertext and TCP/IP protocols) and accessed over the Internet. An intranet is meant fo r the exclusive use of the organization and its associates (customers, employees, members, suppliers, etc.) and is protected from unauthorized access with security systems such as firewalls. It creates a meeting point for sharing knowledge for its users. We use a case study of a communication company to show intra networking as an effective supportive technology for knowledge management

Hippocampal Conceptual Representations and their Reward Value

Hippocampus is critical for fast learning of relational knowledge. Relational knowledge acquired and represented by the hippocampus may include reward associations of arbitrary cues and responses during adaptive decision making. Hippocampal memory representations that are formed in tasks that use reinforcement learning may reflect reward-related signals, but this may not be apparent unless the magnitude of expected reward is controlled. This issue is particularly relevant to a recent study by Kumaran et al. (2009) whose results suggested that the hippocampus may house abstract conceptual knowledge, whereas other brain areas

Contribution of space charges to the polarization of ferroelectric superlattices and its effect on dielectric properties

A theoretical model is developed for ferroelectric bilayers and multilayer heterostructures that employs a nonlinear Landau-Devonshire formalism coupled with a detailed analysis of the depolarizing fields arising from the polarization mismatch across interlayer interfaces and the electrical fields of localized space charges at such interfaces. We first present how space charges alter the free-energy curves of ferroelectrics and then proceed with a numerical analysis for heteroepitaxial (001) PbTiO3-SrTiO3 (PTO-STO) bilayers and (001) superlattice structures on (001) STO substrates. The switchable (ferroelectric) and nonswitchable (built-in) polarizations and the dielectric properties of PTO-STO bilayers and superlattices are calculated as a function of the planar space-charge density and the volume fraction of the PTO layer. Similar to the temperature dependence of a monolithic ferroelectric, there exists a critical volume fraction PTO below which the bilayer or the superlattice is in the paraelectric state. This critical volume fraction is strongly dependent on the density of trapped charges at the interlayer interfaces. For charge-free (001) PTO-STO heteroepitaxial bilayer and superlattices, the critical fraction is 0.40 for both constructs but increases to 0.6 and 0.72, for the bilayer and the superlattice, respectively, for a planar space-charge density of 0.05 C/m(2). Furthermore, our results show that close to the vicinity of ferroelectric-paraelectric phase transition, there is a recovery in ferroelectric polarization. The dielectric-response calculations verify that there is sharp ferroelectric phase transformation for charge-free bilayers and superlattices whereas it is progressively smeared out with an increase in the charge density. Furthermore, our analysis shows that the dielectric constant of these multilayers at a given volume fraction of PTO decreases significantly in the presence of space charges

Actitudes y Experiencias de los Estudiantes de Inglés como Lengua Extranjera de Secundaria en Aulas Equipadas con Tableros Interactivos

The purpose of this study was to examine ninth grade EFL students’ experiences and attitudes towards classrooms equipped with interactive whiteboards (IWB). The data were collected with a questionnaire about attitudes towards IWB use in EFL classes, and observations from three different classrooms in three different high schools. The study indicated that the EFL students were not fully aware of how to use IWBs in learning English although they had a background of IWB use. In addition, there was no statistically significant difference in the attitudes of the male and female students towards using IWBs. Overall, the results revealed that EFL students’ attitudes towards IWBs were positive although there were some technical challenges in IWB classrooms.El propósito de este estudio fue indagar sobre las experiencias y actitudes hacia las aulas equipadas con tableros interactivos de un grupo de estudiantes de inglés como lengua extranjera de noveno grado. Los datos fueron recogidos por medio de un cuestionario para conocer las actitudes de los estudiantes hacia el uso de este tipo de herramienta tecnológica y las observaciones de tres diferentes clases entre tres diferentes colegios. El estudio indicó que los estudiantes de inglés como lengua extranjera no estaban completamente informados de cómo utilizar los tableros interactivos para el aprendizaje del inglés pese a conocer los antecedentes del uso de IWB. Además, no se observaron diferencias significativas en términos estadísticos en relación a las actividades de los estudiantes de género masculino y femenino hacia el uso de IWB. En general, los resultados revelaron que los estudiantes de inglés como lengua extranjera tenían una actitud positiva hacia el uso de IWB a pesar de presentarse algunos problemas técnicos en las aulas

Investıgatıons of some physıcal properties and erosıon tendency of soıl of trabzon lımlı watershed

Bu çalışmada, Trabzon Limli Deresi Yağış Havzası topraklarının bazı fiziksel, hidrofiziksel özellikleri ve erozyon eğilimleri araştırılmıştır. Araştırma havzası Türkiye’nin Doğu Karadeniz Bölgesinde yer almakta olup Trabzon’a 24 km. uzaklıktadır. Bu amaçla 3 farklı yükseklik kademesi ve iki farklı bakıda yer alan tarım ve otlak alanlarında toplam 32 adet toprak profili açılmış ve farklı derinlik kademelerinden (0 -20 cm. ve 20 - 50 cm.) toprak örnekleri alınmıştır. Alınan bu toprak örnekleri üzerinde; Tekstür, toprak fraksiyonları, erozyon eğilimleri, nem sabitleri, geçirgenlik, hacim ağırlığı, dane yoğunluğu, gözenek hacmi, ateşte kayıp ve pH gibi 14 özellik ölçülmüştür. Yapılan analizler sonucunda 3 erozyon eğilim indeksi değerlerine göre topraklar erozyona duyarlı bulunmuştur.In this study, some physical properties and erosion tendency of soils in Trabzon - Limli watershed creek have been studied. The study area, Limli watershed creek, which is located in the East Black Sea Region of Turkey is 24 Km. far away from Trabzon. For this purpose, 32 soil profiles have been dug in 3 different altitudes and 2 different exposures and 64 units soil samples have been taken from different depth steps (0-20 cm. and 20 - 50 cm.). As indicated below, 14 soil properties have been measured on each soil sample; texture, soil fractions, dispersiyon ratio, colloid / moisture equivalent ratio, erosion ratio, loss on ignition ratio and pH. It has been determined that soils are sensitive to erosion, acording to the soil erodibility index