Loop Connections Research Articles

Dynamical balance between excitation and inhibition of feedback neural circuit via inhibitory synaptic plasticity

Cortical cortex is mainly composed of excitatory and inhibitory neurons. Balance between excitation and inhibition is a ubiquitous experimental phenomenon in brain. On the one hand, balanced excitation and inhibition plays a crucial role in maintaining normal brain functions; on the other hand, the loss of balance between the two opposing forces will cause neural diseases, such as epilepsy, Parkinson, schizophrenia, etc. Thus the research on balance between excitation and inhibition increasingly focuses on the field of neuroscience. Feedback neural circuit with recurrent excitatory and inhibitory connections is ubiquitous in cortical cortex. However, it is still little known how to achieve and maintain the balance between excitation and inhibition in feedback neural circuit. In this study it is proposed that inhibitory synaptic plasticity should play a key role in regulating the balance between excitation and inhibition. Firstly, the feedback neural circuit model is constructed using leaky integrate-and-fire neuron model, mainly composed of excitatory feed-forward loop, and excitatory and inhibitory recurrent connections. The proposed inhibitory synaptic model is incorporated into the feedback neural circuit model, and whose mathematical formulation is presented in detail. Secondly, the excitatory and inhibitory synaptic currents are obtained through numerical simulations, which demonstrate that the precise balance between excitation and inhibition is achieved under the regulation of inhibitory synaptic plasticity. Furthermore, the research results show that this balance is robust to the fluctuation inputs and disturbances. Thirdly, the balance mechanism underlined by inhibitory synaptic plasticity is elucidated through theoretical and simulation analysis, separately, which provides a clear explanation and an insight into how to achieve and maintain the balance between excitation and inhibition in a feedback neural circuit. Finally, the numerical results reveal that the neuron numbers in excitatory and inhibitory feedback loop exert an influence on the balance, and the larger number can enhance the balance between excitation and inhibition, which explains, to some extent, why there are dense connections between neurons in brain. The results in this study shed light on the balance mechanism of feedback neural circuit, and provide some clues for understanding the mechanism of balance between excitation and inhibition in the brain area.

A Simple RLCC-Diode-Opamp Chaotic Oscillator

This paper presents a simple autonomous chaotic oscillator. The design method is primarily based on a linear oscillator constructed by a closed loop connection of two building blocks, i.e. an inverting active integrator and a passive second-order LC integrator. A diode is inserted in parallel to the two building blocks for inducing chaos. The mathematical model reveals a set of three-dimensional ordinary differential equations, containing seven terms with four constants and an exponential nonlinearity. The dynamics properties are investigated in terms of an equilibrium point, Jacobian matrix, chaotic attractors, bifurcation, Lyapunov exponents, and chaotic waveforms in time domain. The proposed chaotic oscillator potentially exhibits complex dynamical behaviors through the utilization of only six minimal electronic components.

Structure Based Grading of Kinematic Chains

Kinematic chains differ due to the structural differences between them. The location of links, joints and loops differ in each kinematic chain to make it unique. Two similar kinematic chains will produce similar motion properties and hence are avoided. The performance of these kinematic chains also depends on the individual topology, i.e. the placement of its entities. In the present work an attempt has been made to compare a family of kinematic chains based on its structural properties. The method is based on identifying the chains structural property by using its JOINT LOOP connectivity table. Nomenclature J - Number of joints, F - Degree of freedom of the chain, N - Number of links, L - Number of basic loops (independent loops plus one peripheral loop).

Steady-State Harmonic Domain Matrix-Based Modeling of Four-Quadrant EMU Line Converter

As a non-linear time variant system, the four-quadrant line converter of an electric multiple unit (EMU) was expressed by linear time periodic functions near an operating point and modeled by a steady-state harmonic domain matrix. The components were then combined according to the circuit connection and relations of the feedback control loops to form a complete converter model. The proposed modeling method allows the study of the amplitude of harmonic impedances to explore harmonic coupling. Moreover, the proposed method helps provide a better design for the converter controllers, as well as solves the problem in coordination operation between the EMUs and the AC supply. On-site data from an actual <TEX>$CRH_2$</TEX> high-speed train were used to validate the modeling principles presented in the paper.

Loop connection with fibre-reinforced precast concrete components in tension

Overlapping of reinforcement bars or loops is often used to connect precast members. The precast units have projecting bars, usually with a full 180° hook, which are embedded in situ in concrete after erection. This paper studies a tension joint using direct overlapping loops, evaluating the influence of the addition of steel fibres to the in situ concrete. Other variables studied were the diameter of the loop bend and the presence of transverse reinforcement in the loop. The results indicate the possibility of reducing the joint width between precast elements by using steel fibres. An expression based on strut and tie theory is proposed to calculate the connection’s strength, and it provided a good approximation to the experimental results.

Structural Brain Connectivity in School-Age Preterm Infants Provides Evidence for Impaired Networks Relevant for Higher Order Cognitive Skills and Social Cognition.

Extreme prematurity and pregnancy conditions leading to intrauterine growth restriction (IUGR) affect thousands of newborns every year and increase their risk for poor higher order cognitive and social skills at school age. However, little is known about the brain structural basis of these disabilities. To compare the structural integrity of neural circuits between prematurely born controls and children born extreme preterm (EP) or with IUGR at school age, long-ranging and short-ranging connections were noninvasively mapped across cortical hemispheres by connection matrices derived from diffusion tensor tractography. Brain connectivity was modeled along fiber bundles connecting 83 brain regions by a weighted characterization of structural connectivity (SC). EP and IUGR subjects, when compared with controls, had decreased fractional anisotropy-weighted SC (FAw-SC) of cortico-basal ganglia-thalamo-cortical loop connections while cortico-cortical association connections showed both decreased and increased FAw-SC. FAw-SC strength of these connections was associated with poorer socio-cognitive performance in both EP and IUGR children.

CFRP-Aluminium Structures Realized by Laser Beam Joining Process

Modern lightweight structures containing hybrid materials allow an improvement of the weight-specific properties. However, to exploit the potential as far as possible novel joint concepts are necessary, enabling an economic structure manufacturing. The DFG-researcher group Schwarz-Silber (FOR 1224) at the University of Bremen aims to explore and develop interface structures for advanced FRP-Al compounds. Considering textile, welding and casting techniques novel joint concepts are under development, in five interdisciplinary projects. Within their work the researcher group focuses on three concepts realizing the transition structures: the usage of wires (titanium), foils (titanium) and fibres (glass fibre) as transition elements between CFRP and aluminium. Typical examples for such hybrid structures can be found in products from the aerospace industry (e.g. hull segments), the car industry (e.g. CFRP roof structures), but also in general mechanical engineering (e.g. rotor blade elements). In this paper, the joint configuration based on titanium wires and a laser beam conduction welding process will be presented. As beam source a lamp pumped Nd:YAG laser (HL4006D) was used. First specimens obtained will be discussed with respect to their properties. It will be shown that the novel approach is in principle suitable to produce load-bearing CFRP-aluminium structures. The wire concept represents a parallel arrangement of miniaturized loop connections. It is characterized by joining a CF-Ti-textile to an aluminium sheet. A carbon fibre loop is threaded through a titanium wire loop by textile technologies on one side. On the side opposite to the CF, the titanium wire loops of the CF-Ti-textile are joined to an aluminium component by welding or casting. A double-sided laser beam heat conduction welding process was applied, for both concepts. During processing, the laser beam was travels along the aluminium edge. The titanium-aluminium structure is welded in two steps. During the first step (i.e. the first weld pass) the aluminium and titanium are heated by the defocused laser beam simultaneously on both sides. An aluminium melt pool is formed, supported by the action of gravity and a certain amount of pre-heating of the titanium-wire or the titanium-foils by the laser beam and by heat conduction through the aluminium melt pool. In the second, immediately subsequent step (i.e. the second weld pass), due to a pre-heating of the materials by the first pass and an increased heat transfer between both materials, a complete wetting of the titanium structures in the joining zone is achieved.

Intra-molecular G-quadruplex structure generated by DNA-templated click chemistry: “Turn-on” fluorescent probe for copper ions

A novel homogenous fluorescent sensor for signal-on detection of Cu2+ has been developed based on intra-molecular G-quadruplex formed by DNA-templated click reaction and crystal violet (CV) as label-free signal reporter. The clickable DNA probe consists of two G-rich strands (A and B) bearing azide and alkyne group, respectively, and a template strand (C) locating two proximate reactants by pairing with A and B. The sequences of A and B are derived from asymmetric split of the G-quadruplex sequence (TTAGGG)4. In the presence of Cu2+, the whole G-quadruplex sequence A–B is generated by chemical ligation of A and B via copper ion-catalyzed alkyne-azide cycloaddition, then released from template by toehold strand displacement, and consequently forming a stable intra-molecular G-quadruplex, which binds with CV to generate a strong fluorescent signal. Oppositely, weak fluorescence was obtained without Cu2+ because of unstable intermolecular G-quadruplex formed by A and B and lack of lateral loop connection. Therefore, the Cu2+ can be sensitively and specifically detected by the fluorescence of the CV-stained G-quadruplex with a low detection limit of 65nM and a linear range of 0.1–3µM. This method rationally integrated the DNA-templated synthesis and G-quadruplex structure-switch, presenting a simple and promising approach for biosensor development.

Reduced functional connectivity within the limbic cortico‐striato‐thalamo‐cortical loop in unmedicated adults with obsessive‐compulsive disorder

Cortico-striato-thalamo-cortical (CSTC) loops project from the cortex to the striatum, then from the striatum to the thalamus via the globus pallidus, and finally from the thalamus back to the cortex again. These loops have been implicated in Obsessive-Compulsive Disorder (OCD) with particular focus on the limbic CSTC loop, which encompasses the orbitofrontal and anterior cingulate cortices, as well as the ventral striatum. Resting state functional-connectivity MRI (rs-fcMRI) studies, which examine temporal correlations in neural activity across brain regions at rest, have examined CSTC loop connectivity in patients with OCD and suggest hyperconnectivity within these loops in medicated adults with OCD. We used rs-fcMRI to examine functional connectivity within CSTC loops in unmedicated adults with OCD (n = 23) versus healthy controls (HCs) (n = 20). Contrary to prior rs-fcMRI studies in OCD patients on medications that report hyperconnectivity in the limbic CSTC loop, we found that compared with HCs, unmedicated OCD participants had reduced connectivity within the limbic CSTC loop. Exploratory analyses revealed that reduced connectivity within the limbic CSTC loop correlated with OCD symptom severity in the OCD group. Our finding of limbic loop hypoconnectivity in unmedicted OCD patients highlights the potential confounding effects of antidepressants on connectivity measures and the value of future examinations of the effects of pharmacological and/or behavioral treatments on limbic CSTC loop connectivity.

Estimating broadband diffusion in the EU using NUTS 1 regional data

In this paper we use panel data on NUTS 1 regional data for 27 EU countries in the years 2006–2010 to analyze determinants of broadband diffusion. We estimate both linear demand specification and the logistic diffusion function. We find that, after controlling for regional differences due to socioeconomic factors, inter-platform competition approximated by an inter-platform Herfindahl index has a significant positive impact on broadband diffusion. Broadband deployment is lower in countries in which DSL has a greater share in Internet access and it is higher in countries in which cable modem has a greater share in Internet access. Moreover, we find that competition between DSL providers has a significant and positive impact on broadband penetration. First, higher prices for a fully unbundled local loop connection, which represent the cost of providing copper-based Internet services, have a significant and negative impact on broadband penetration. Second, a greater incumbent share in DSL connections has a significant and negative impact on broadband penetration.

Tests and limit analysis of loop connections between precast concrete elements loaded in tension

This paper deals with loop connections loaded in tension. Such connections; also known as U-bar joints, are frequently used in practice to establish continuity between precast deck elements in steel–concrete composite bridges. The tensile strength of a loop connection may either be governed by yielding of the U-bars or by failure in the joint concrete. Only few investigations of the case of concrete failure can be found in the literature. This paper presents an experimental program dedicated to study loop connections critical to concrete failure. The results show that the ultimate load is influenced by important design parameters such as the overlapping length of the U-bars, the spacing between adjacent U-bars and the amount of transverse reinforcement. Knowledge about the parameters that have an effect on the failure of the joint concrete is important in order to avoid this failure mode in practice. The paper also presents an upper bound plasticity model, which is able to capture the experimental tendencies in a satisfactory manner. Finally, the paper includes discussions of how the presented research may be utilized in practice to design connections that are able to transfer the full yield strength of the connecting precast elements.

Disrupted connectivity of motor loops in Parkinson's disease during self-initiated but not externally-triggered movements

Parkinson's disease (PD) reportedly includes altered connectivity of neural loops involving the basal ganglia and cerebellum, although little is known regarding any changes in the connectivity of motor loops. The goal of this study was to further understand the connectivity within the basal ganglia–thalamo-motor (BGTM) and cerebro-cerebellar (CC) loops in PD. Twelve PD patients and 12 age-matched control subjects performed a protocol involving self-initiated (SI) and externally-triggered (ET) finger movements, while being scanned with functional magnetic resonance imaging. Compared with the control subjects, the PD subjects showed hypo-activation in the bilateral putamen, right supplementary motor area and hyper-activation in the right premotor cortex. In the sensorimotor cortex and cerebellar hemisphere, PD subjects tended to show hyper-activation in a main effects analysis, but hypo-activation in a linear effects analysis. Analysis using structural equation modeling (SEM) revealed significant positive interactions within the right BGTM loop during the SI task and within the right (right cerebral hemisphere–left cerebellum) CC loop during the ET task. SEM also revealed task-related quantitative changes between the thalamus and the motor cortices in the control subjects. We found that the PD patients showed reduced connectivity in the right BGTM loop and inter-hemispheric connections in SEM, which is the first demonstration of this phenomenon. Interestingly, PD patients exhibited preserved connectivity within the right CC loop during the ET task. These results suggest disruption of cortico-striatal processing and preservation of relatively intact neural circuits that do not involve the basal ganglia in PD.

Manufacturing and Analysis of Loop Connections for Thermoplastic Composites

Short cycle times and a high level of automation are outstanding features of manufacturing processes with thermoplastic composites. Additionally, the repeatable formability and weldability of thermoplastics enables adapted joining techniques like warm-shaped loop connections. This paper covers studies on the manufacturing of loop connections, performed during stamp forming of the composite structure. Simple loop joints with flat welding zones are analysed both, experimentally and numerically. Based on that, improvement strategies to optimise the loading behaviour are discussed and loop connections with profiled welding zones are designed to improve the peel resistance. For validation of the design concept, numerical analyses are conducted using an enhanced material definition including failure mode dependent stiffness degradation. Additional processing studies and mechanical tests are used to evaluate the adapted joint design, demonstrating the improved load bearing behaviour.

The visual corticostriatal loop through the tail of the caudate: circuitry and function

Although high level visual cortex projects to a specific region of the striatum, the tail of the caudate, and participates in corticostriatal loops, the function of this visual corticostriatal system is not well understood. This article first reviews what is known about the anatomy of the visual corticostriatal loop across mammals, including rodents, cats, monkeys, and humans. Like other corticostriatal systems, the visual corticostriatal system includes both closed loop components (recurrent projections that return to the originating cortical location) and open loop components (projections that terminate in other neural regions). The article then reviews what previous empirical research has shown about the function of the tail of the caudate. The article finally addresses the possible functions of the closed and open loop connections of the visual loop in the context of theories and computational models of corticostriatal function.

Influence Of Textile Process Parameter On Joint Strength For Integral CFRP-Aluminum Transition Structures

With increasing application of hybrid structures a novel joining technology is required in terms of lightweight design. For joining CFRP (carbon fiber reinforced plastics) and metal components in load application zones, the conventional method of riveting is often applied, which is not suitable to the material. Within the investigations of the research group “Schwarz- Silber” (FOR1224) funded by the DFG (German Research Foundation) novel transition structures for aluminum-CFRP joints are investigated with view to weight, strength and a lean integral structure. This paper deals with the influence of the textile process on the joint strength. The process parameter pretension, which is defined by the manufacturing process of loop connections for aluminum-CFRP joints, is identified. A suitable material combination for the loop is determined and the influence of the loop's pretension on the joint strength is analyzed.

Recent Developments for Laser Beam Joining of CFRP-aluminum Structures

Modern lightweight structures including dissimilar materials allow an improvement of the weight-specific properties. However, novel joining concepts are necessary to exploit the potential and to enable efficient manufacturing. The DFG research group “Schwarz-Silber” (FOR1224) aims to develop and investigate transition structures for advanced CFRP-aluminum connections. In five interdisciplinary projects novel concepts are under development considering textile, welding, brazing and casting techniques. Within their work the research group focuses on three approaches realizing the transition: the usage of wires (titanium), foils (titanium) and fibers (glass fiber) as transition elements between CFRP and aluminum. The “wire concept” represents a parallel arrangement of miniaturized loop connections. Carbon fibers are threaded through titanium wire loops which are joined to an aluminum component by a combined laser welding-brazing process. The “foil concept” is based on titanium laminates. This concept is characterized by joining a Ti-CFRP laminate to an aluminum sheet. This hybrid laminate, in which CFRP-layers alternate with titanium foils, has been fabricated. The titanium side of the laminate is joined to the aluminum sheet. In this paper, the joint configurations based on titanium wires and foils are presented. First specimens are discussed with respect to their properties. It is shown that the novel approaches are principally suitable to produce advanced CFRP-aluminum structures by using laser beam processes.

Heptagons in C68: Impact on Stabilities, Growth, and Exohedral Derivatization of Fullerenes

Density functional investigations have been performed on C68 fullerene set and related exohedral derivatives. All of the heptagon-containing isomers are systematically studied, and a hepta-C68 (namely, by C68_id146:C1) is predicted to be the most thermodynamically favorable framework, which accords with the experimental results. To clarify the growth mechanism from C68 to C70, a novel loop–loop connection between C68 and C70 has been proposed, and an unreported C68_id9:Cs is proven to be the most favorable parent molecule to afford the well-known #8149C70:D5h with a barrier of 2.16 eV. In comparison, 6.01 eV is required if C68_id146:C1 is selected as the starting point. Besides the hollow cages, the negative formation energies and the large HOMO–LUMO gaps of C68_id146X6 (X: H, F, Cl) imply that hydrogenation, fluorination, and chlorination are all feasible ways to stabilize the carbon cage. Moreover, the regioselectivity and sequence of chlorination sites are discussed to elucidate the selective synthesis...

Loop spaces and connections

We examine the geometry of loop spaces in derived algebraic geometry and extend in several directions the well-known connection between rotation of loops and the de Rham differential. Our main result, a categorification of the geometric description of cyclic homology, relates S1-equivariant quasicoherent sheaves on the loop space of a smooth scheme or geometric stack X in characteristic zero with sheaves on X with flat connection, or equivalently DX-modules. By deducing the Hodge filtration on de Rham modules from the formality of cochains on the circle, we are able to recover DX-modules precisely rather than a periodic version. More generally, we consider the rotated Hopf fibration Ω S3→Ω S2→S1, and relate Ω S2-equivariant sheaves on the loop space with sheaves on X with arbitrary connection, with curvature given by their Ω S3-equivariance.

Auditory thalamic reticular nucleus of the rat: Anatomical nodes for modulation of auditory and cross‐modal sensory processing in the loop connectivity between the cortex and thalamus

The auditory sector of the thalamic reticular nucleus (TRN) plays a pivotal role in gain and/or gate control of auditory input relayed from the thalamus to cortex. The TRN is also likely involved in cross-modal sensory processing for attentional gating function. In the present study, we anatomically examined how cortical and thalamic afferents intersect in the auditory TRN with regard to these two functional pathways. Iontophoretic injections of biocytin into subregions of the auditory TRN, which were made with the guidance of electrophysiological recording of auditory response, resulted in retrograde labeling of cortical and thalamic cells, indicating the sources of afferents to the TRN. Cortical afferents from area Te1 (temporal cortex, area 1), which contains the primary and anterior auditory fields, topographically intersected thalamic afferents from the ventral division of the medial geniculate nucleus at the subregions of the auditory TRN, suggesting tonotopically organized convergence of afferents, although they innervated a given small part of the TRN from large parts. In the caudodorsal and rostroventral parts of the auditory TRN, cortical afferents from nonprimary visual and somatosensory areas intersected thalamic afferents from auditory, visual, and somatosensory nuclei. Furthermore, afferents from the caudal insular cortex and the parvicellular part of the ventral posterior thalamic nucleus, which are associated with visceral processing, converged to the rostroventral end of the auditory TRN. The results suggest that the auditory TRN consists of anatomical nodes that mediate tonotopic and/or cross-modal modulation of auditory and other sensory processing in the loop connectivity between the cortex and thalamus.

Insight into G-DNA Structural Polymorphism and Folding from Sequence and Loop Connectivity through Free Energy Analysis

The lengths of G-tracts and their connecting loop sequences determine G-quadruplex folding and stability. Complete understanding of the sequence–structure relationships remains elusive. Here, single-loop G-quadruplexes were investigated using explicit solvent molecular dynamics (MD) simulations to characterize the effect of loop length, loop sequence, and G-tract length on the folding topologies and stability of G-quadruplexes. Eight loop types, including different variants of lateral, diagonal, and propeller loops, and six different loop sequences [d0 (i.e., no intervening residues in the loop), dT, dT2, dT3, dTTA, and dT4] were considered through MD simulation and free energy analysis. In most cases the free energetic estimates agree well with the experimental observations. The work also provides new insight into G-quadruplex folding and stability. This includes reporting the observed instability of the left propeller loop, which extends the rules for G-quadruplex folding. We also suggest a plausible explanation why human telomere sequences predominantly form hybrid-I and hybrid-II type structures in K+ solution. Overall, our calculation results indicate that short loops generally are less stable than longer loops, and we hypothesize that the extreme stability of sequences with very short loops could possibly derive from the formation of parallel multimers. The results suggest that free energy differences, estimated from MD and free energy analysis with current force fields and simulation protocols, are able to complement experiment and to help dissect and explain loop sequence, loop length, and G-tract length and orientation influences on G-quadruplex structure.