THE REGULATION AND PACKAGING OF SYNAPTIC VESICLES RELATED TO RECRUITMENT WITHIN CRAYFISH AND FRUIT FLY NEUROMUSCULAR JUNCTIONS: VARIATIONS IN LOW- AND HIGH-OUTPUT TERMINALS

Glutamate is the main excitatory neurotransmitter in the CNS and at the neuromuscular junctions (NMJs) of invertebrate. The characteristic similarities to CNS glutamatergic synapses in vertebrate and the anatomical simplicity of invertebrate NMJs favor the investigation of glutamatergic synaptic functions in this system. This dissertation mainly aimed to physiologically separate two functional vesicle groups, the reserve pool (RP) and readily releasable pool (RRP) within presynaptic nerve terminals of Procambarus Clarkii and Drosophila melanogaster. This was addressed in part by blocking the vesicular glutamate transporter (VGlut) with bafilomycin A1. Various frequencies of motor nerve stimulation, exposure time, and concentration of bafilomycin A1 were examined. The low-output tonic opener NMJs in crayfish exposed to 4μM bafilomycin A1 and 20Hz continuous stimulation decreased the EPSP amplitude to 50% in ∼30min with controls lasting 3h. After activity and bafilomycin A1-induced synaptic depression, the EPSPs were rapidly revitalized by serotonin (5-HT, 1μM) in the crayfish preparations. The 5-HT action can be blocked almost completely with a PLC inhibitor, but partially with a cAMP activator. The higher output synapses of the larval Drosophila NMJ when stimulated at 1Hz or 5Hz and exposed to 4μM of bafilomycin A1 showed a depression rate of 50% within ∼10min with controls lasting ∼40min. After low frequency depression and/or exposure to bafilomycin A1 a burst of higher frequency (10Hz) can recruit vesicles from the RP to the RRP. Physiological differences in low- (tonic like) and high-output (phasic like) synapses match many of the expected anatomical features of these terminals, part of this dissertation highlights physiological differences and differential modulation and/or extent of the vesicles in a RP for maintaining synaptic output during evoked depression of the RRP in crayfish abdomen extensor preparation. With the use of bafilomycin A1, the tonic terminal is fatigue resistant due to a large RRP, whereas the phasic depresses rapidly upon continuous stimulation. Upon depression of the tonic terminal, 5-HT has a large RP to act on to recruit vesicles to the RRP; whereas, the phasic terminal, 5-HT can recruit RP vesicles to the RRP prior to synaptic depression but not after depression

Effects of Finite Deformed Length in Carbon Nanotubes

The effect of finite deformed length is demonstrated by squashing an armchair (10,10) single-walled carbon nanotube with two finite tips. Only when the deformed length is long enough, an effectual metal-semiconductor-metal heterojunction can be formed in the metallic tube. The effect of finite deformed length is explained by the quantum tunnelling effect. Furthermore, some conceptual designs of nanoscale devices are proposed from the metal-semiconductor-metal heterojunction.Comment: 4 pages, 4 figure

Converting normal insulators into topological insulators via tuning orbital levels

Tuning the spin-orbit coupling strength via foreign element doping and/or modifying bonding strength via strain engineering are the major routes to convert normal insulators to topological insulators. We here propose an alternative strategy to realize topological phase transition by tuning the orbital level. Following this strategy, our first-principles calculations demonstrate that a topological phase transition in some cubic perovskite-type compounds CsGeBr$_3$ and CsSnBr$_3$ could be facilitated by carbon substitutional doping. Such unique topological phase transition predominantly results from the lower orbital energy of the carbon dopant, which can pull down the conduction bands and even induce band inversion. Beyond conventional approaches, our finding of tuning the orbital level may greatly expand the range of topologically nontrivial materials

Utility-maximization Resource Allocation for Device-to-Device Communication Underlaying Cellular Networks

Device-to-device(D2D) underlaying communication brings great benefits to the cellular networks from the improvement of coverage and spectral efficiency at the expense of complicated transceiver design. With frequency spectrum sharing mode, the D2D user generates interference to the existing cellular networks either in downlink or uplink. Thus the resource allocation for D2D pairs should be designed properly in order to reduce possible interference, in particular for uplink. In this paper, we introduce a novel bandwidth allocation scheme to maximize the utilities of both D2D users and cellular users. Since the allocation problem is strongly NP-hard, we apply a relaxation to the association indicators. We propose a low-complexity distributed algorithm and prove the convergence in a static environment. The numerical result shows that the proposed scheme can significant improve the performance in terms of utilities.The performance of D2D communications depends on D2D user locations, the number of D2D users and QoS(Quality of Service) parameters