Surface Analysis of OFE-Copper X-Band Accelerating Structures and Possible Correlation to RF Breakdown Events

X-band accelerator structures meeting the Next Linear Collider (NLC) design requirements have been found to suffer vacuum surface damage caused by radio frequency (RF) breakdown, when processed to high electric-field gradients. Improved understanding of these breakdown events is desirable for the development of structure designs, fabrication procedures, and processing techniques that minimize structure damage. RF reflected wave analysis and acoustic sensor pickup have provided breakdowns localization in RF structures. Particle contaminations found following clean autopsy of four RF-processed travelling wave structures, have been catalogued and analyzed. Their influence on RF breakdown, as well as that of several other material-based properties, will be discussed.Comment: 21 pages, 8 figures, 4 tables, Submitted to JVST A as a proceeding of the 50th AVS conference (Baltimore, MD, 2-7 Nov 2003

Sparse and Dense Encoding in Layered Associative Network of Spiking Neurons

A synfire chain is a simple neural network model which can propagate stable synchronous spikes called a pulse packet and widely researched. However how synfire chains coexist in one network remains to be elucidated. We have studied the activity of a layered associative network of Leaky Integrate-and-Fire neurons in which connection we embed memory patterns by the Hebbian Learning. We analyzed their activity by the Fokker-Planck method. In our previous report, when a half of neurons belongs to each memory pattern (memory pattern rate $F=0.5$), the temporal profiles of the network activity is split into temporally clustered groups called sublattices under certain input conditions. In this study, we show that when the network is sparsely connected ($F<0.5$), synchronous firings of the memory pattern are promoted. On the contrary, the densely connected network ($F>0.5$) inhibit synchronous firings. The sparseness and denseness also effect the basin of attraction and the storage capacity of the embedded memory patterns. We show that the sparsely(densely) connected networks enlarge(shrink) the basion of attraction and increase(decrease) the storage capacity

Влияние электрического поля на адгезионные характеристики системы полихлоропрен-шунгит

The effect of temperature and external electric field on the adhesion characteristics in the polychloroprene-schungite system was investigated. It is shown that an increase in temperature and orientation of macromolecules of polychloroprene in an external electric field significantly increase the bond strength between the studied components. The detected effects are explained from the viewpoint of the possibility of direct chemical interaction ofshungite with polychloroprene macromolecules oriented in a certain way in the region of an adhesive compound formation. This is facilitated by the structural features of schungite (the presence of paramagnetic centers, fullerene-like structures, metal oxides) and polychloroprene in shungite, as well as by the creation of the most optimal modes for implementing this interaction. To assess the strength of the interaction between polychloroprene and the surface of shungite we used a method for determining the stress of exfoliation of a polymer film from the surface of a shungite plate. It was established that the greatest effect in strengthening the bond between polychloroprene and the surface of shungite is achieved when a polymer film is formed from a solution in carbon tetrachloride on a negative electrode (cathode). The strength of the bond between shungite and the polychloroprene film formed on the cathode is more than two times higher than this parameter when forming the same film on the anode. The energy expended during the peeling of a film formed on the cathode is twice the energy of exfoliation from the shungite plate of the film formed on the anode. The analysis of the change in the supramolecular structure of polychloroprene in the polychloroprene-shungite system as a result of the orientational influence of an external electrostatic field was carried out using the temperature dependence of the tangent of the dielectric loss angle of the systems under study. It is shown that a polychloroprene film formed in an electrostatic field has a more ordered structure compared to a similar sample formed without a field. This fact is evidenced by the shift of the maxima toward higher temperatures in the relaxation spectra of the dipole polarization for the system formed without the field, and the system formed on the cathode. The polychloroprene film containing finely dispersed shungite as a filler and formed on the cathode is characterized by an increased value of the tangent of dielectric loss angle and an increased number of peaks of dipole relaxation in the temperature range studied.Исследовано влияние температуры и внешнего электрического поля на адгезионные характеристики в системе полихлоропрен-шунгит. Показано, что повышение температуры и ориентация макромолекул полихлоропрена во внешнем электрическом поле существенно увеличивают прочность связи между исследованными компонентами. Обнаруженные эффекты, объяснены с точки зрения возможности непосредственного химического взаимодействия шунгита с ориентированными определенным образом макромолекулами полихлоропрена в области формирования адгезионного соединения. Этому способствуют особенности строения шунгита (наличие в шунгите парамагнитных центров, фуллереноподобных структур, оксидов металлов) и полихлоропрена, являющегося полярным эластомером, а также создание оптимальных режимов для реализации такого взаимодействия. Для оценки прочности взаимодействия между полихлоропреном и поверхностью шунгита в работе использован метод определения напряжения отслаивания полимерной пленки от поверхности шунгитовой пластинки. Установлено, что наибольший эффект в упрочнении связи между полихлоропреном и поверхностью шунгита достигается при формировании полимерной пленки из раствора в четыреххлористом углероде на отрицательном электроде (катоде). Прочность связи шунгита с полихлоропреновой пленкой, сформированной на катоде, более, чем в два раза превышает этот параметр при формировании такой же пленки на аноде. Анализ изменения надмолекулярной структуры полихлоропрена в системе полихлоропрен-шунгит в результате ориентационного воздействия внешнего электростатического поля произведен с помощью температурной зависимости тангенса угла диэлектрических потерь исследуемых систем. Показано, что пленка полихлоропрена, сформированная в электростатическом поле, имеет более упорядоченную структуру по сравнению с аналогичным образцом, но сформированном без поля. Об этом факте свидетельствует сдвиг максимумов в сторону больших температур в спектрах релаксации дипольной поляризации для системы, сформированной без воздействия поля, и системы, сформированной на катоде. Пленка полихлоропрена, содержащая в качестве наполнителя мелкодисперсный шунгит и сформированная на катоде, характеризуется повышенным значением тангенса угла диэлектрических потерь и увеличенным количеством пиков дипольной релаксации в исследованной температурной области

Chronic Toxoplasma Infection Modifies the Structure and the Risk of Host Behavior

The intracellular parasite Toxoplasma has an indirect life cycle, in which felids are the definitive host. It has been suggested that this parasite developed mechanisms for enhancing its transmission rate to felids by inducing behavioral modifications in the intermediate rodent host. For example, Toxoplasma-infected rodents display a reduction in the innate fear of predator odor. However, animals with Toxoplasma infection acquired in the wild are more often caught in traps, suggesting that there are manipulations of intermediate host behavior beyond those that increase predation by felids. We investigated the behavioral modifications of Toxoplasma-infected mice in environments with exposed versus non-exposed areas, and found that chronically infected mice with brain cysts display a plethora of behavioral alterations. Using principal component analysis, we discovered that most of the behavioral differences observed in cyst-containing animals reflected changes in the microstructure of exploratory behavior and risk/unconditioned fear. We next examined whether these behavioral changes were related to the presence and distribution of parasitic cysts in the brain of chronically infected mice. We found no strong cyst tropism for any particular brain area but found that the distribution of Toxoplasma cysts in the brain of infected animals was not random, and that particular combinations of cyst localizations changed risk/unconditioned fear in the host. These results suggest that brain cysts in animals chronically infected with Toxoplasma alter the fine structure of exploratory behavior and risk/unconditioned fear, which may result in greater capture probability of infected rodents. These data also raise the possibility that selective pressures acted on Toxoplasma to broaden its transmission between intermediate predator hosts, in addition to felid definitive hosts

Impairment of Adolescent Hippocampal Plasticity in a Mouse Model for Alzheimer's Disease Precedes Disease Phenotype

The amyloid precursor protein (APP) was assumed to be an important neuron-morphoregulatory protein and plays a central role in Alzheimer's disease (AD) pathology. In the study presented here, we analyzed the APP-transgenic mouse model APP23 using 2-dimensional gel electrophoresis technology in combination with DIGE and mass spectrometry. We investigated cortex and hippocampus of transgenic and wildtype mice at 1, 2, 7 and 15 months of age. Furthermore, cortices of 16 days old embryos were analyzed. When comparing the protein patterns of APP23 with wildtype mice, we detected a relatively large number of altered protein spots at all age stages and brain regions examined which largely preceded the occurrence of amyloid plaques. Interestingly, in hippocampus of adolescent, two-month old mice, a considerable peak in the number of protein changes was observed. Moreover, when protein patterns were compared longitudinally between age stages, we found that a large number of proteins were altered in wildtype mice. Those alterations were largely absent in hippocampus of APP23 mice at two months of age although not in other stages compared. Apparently, the large difference in the hippocampal protein patterns between two-month old APP23 and wildtype mice was caused by the absence of distinct developmental changes in the hippocampal proteome of APP23 mice. In summary, the absence of developmental proteome alterations as well as a down-regulation of proteins related to plasticity suggest the disturption of a normally occurring peak of hippocampal plasticity during adolescence in APP23 mice. Our findings are in line with the observation that AD is preceded by a clinically silent period of several years to decades. We also demonstrate that it is of utmost importance to analyze different brain regions and different age stages to obtain information about disease-causing mechanisms

Statistical Significance of Precisely Repeated Intracellular Synaptic Patterns

Can neuronal networks produce patterns of activity with millisecond accuracy? It may seem unlikely, considering the probabilistic nature of synaptic transmission. However, some theories of brain function predict that such precision is feasible and can emerge from the non-linearity of the action potential generation in circuits of connected neurons. Several studies have presented evidence for and against this hypothesis. Our earlier work supported the precision hypothesis, based on results demonstrating that precise patterns of synaptic inputs could be found in intracellular recordings from neurons in brain slices and in vivo. To test this hypothesis, we devised a method for finding precise repeats of activity and compared repeats found in the data to those found in surrogate datasets made by shuffling the original data. Because more repeats were found in the original data than in the surrogate data sets, we argued that repeats were not due to chance occurrence. Mokeichev et al. (2007) challenged these conclusions, arguing that the generation of surrogate data was insufficiently rigorous. We have now reanalyzed our previous data with the methods introduced from Mokeichev et al. (2007). Our reanalysis reveals that repeats are statistically significant, thus supporting our earlier conclusions, while also supporting many conclusions that Mokeichev et al. (2007) drew from their recent in vivo recordings. Moreover, we also show that the conditions under which the membrane potential is recorded contributes significantly to the ability to detect repeats and may explain conflicting results. In conclusion, our reevaluation resolves the methodological contradictions between Ikegaya et al. (2004) and Mokeichev et al. (2007), but demonstrates the validity of our previous conclusion that spontaneous network activity is non-randomly organized

Significance of Input Correlations in Striatal Function

The striatum is the main input station of the basal ganglia and is strongly associated with motor and cognitive functions. Anatomical evidence suggests that individual striatal neurons are unlikely to share their inputs from the cortex. Using a biologically realistic large-scale network model of striatum and cortico-striatal projections, we provide a functional interpretation of the special anatomical structure of these projections. Specifically, we show that weak pairwise correlation within the pool of inputs to individual striatal neurons enhances the saliency of signal representation in the striatum. By contrast, correlations among the input pools of different striatal neurons render the signal representation less distinct from background activity. We suggest that for the network architecture of the striatum, there is a preferred cortico-striatal input configuration for optimal signal representation. It is further enhanced by the low-rate asynchronous background activity in striatum, supported by the balance between feedforward and feedback inhibitions in the striatal network. Thus, an appropriate combination of rates and correlations in the striatal input sets the stage for action selection presumably implemented in the basal ganglia

Omega-3 Fatty Acids from Fish Oil Lower Anxiety, Improve Cognitive Functions and Reduce Spontaneous Locomotor Activity in a Non-Human Primate

Omega-3 (ω3) polyunsaturated fatty acids (PUFA) are major components of brain cells membranes. ω3 PUFA-deficient rodents exhibit severe cognitive impairments (learning, memory) that have been linked to alteration of brain glucose utilization or to changes in neurotransmission processes. ω3 PUFA supplementation has been shown to lower anxiety and to improve several cognitive parameters in rodents, while very few data are available in primates. In humans, little is known about the association between anxiety and ω3 fatty acids supplementation and data are divergent about their impact on cognitive functions. Therefore, the development of nutritional studies in non-human primates is needed to disclose whether a long-term supplementation with long-chain ω3 PUFA has an impact on behavioural and cognitive parameters, differently or not from rodents. We address the hypothesis that ω3 PUFA supplementation could lower anxiety and improve cognitive performances of the Grey Mouse Lemur (Microcebus murinus), a nocturnal Malagasy prosimian primate. Adult male mouse lemurs were fed for 5 months on a control diet or on a diet supplemented with long-chain ω3 PUFA (n = 6 per group). Behavioural, cognitive and motor performances were measured using an open field test to evaluate anxiety, a circular platform test to evaluate reference spatial memory, a spontaneous locomotor activity monitoring and a sensory-motor test. ω3-supplemented animals exhibited lower anxiety level compared to control animals, what was accompanied by better performances in a reference spatial memory task (80% of successful trials vs 35% in controls, p<0.05), while the spontaneous locomotor activity was reduced by 31% in ω3-supplemented animals (p<0.001), a parameter that can be linked with lowered anxiety. The long-term dietary ω3 PUFA supplementation positively impacts on anxiety and cognitive performances in the adult mouse lemur. The supplementation of human food with ω3 fatty acids may represent a valuable dietary strategy to improve behavioural and cognitive functions

Coherence Potentials Encode Simple Human Sensorimotor Behavior

Recent work has shown that large amplitude negative periods in the local field potential (nLFPs) are able to spread in saltatory manner across large distances in the cortex without distortion in their temporal structure forming ‘coherence potentials’. Here we analysed subdural electrocorticographic (ECoG) signals recorded at 59 sites in the sensorimotor cortex in the left hemisphere of a human subject performing a simple visuomotor task (fist clenching and foot dorsiflexion) to understand how coherence potentials arising in the recordings relate to sensorimotor behavior. In all behaviors we found a particular coherence potential (i.e. a cascade of a particular nLFP wave pattern) arose consistently across all trials with temporal specificity. During contrateral fist clenching, but not the foot dorsiflexion or ipsilateral fist clenching, the coherence potential most frequently originated in the hand representation area in the somatosensory cortex during the anticipation and planning periods of the trial, moving to other regions during the actual motor behavior. While these ‘expert’ sites participated more consistently, other sites participated only a small fraction of the time. Furthermore, the timing of the coherence potential at the hand representation area after onset of the cue predicted the timing of motor behavior. We present the hypothesis that coherence potentials encode information relevant for behavior and are generated by the ‘expert’ sites that subsequently broadcast to other sites as a means of ‘sharing knowledge’