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In this paper, we discuss the surface modification of spinel LiMn2O4 cathodes by MnO2 particles via a simple precipitation method at room temperature, without any heat treatment. Nanosized MnO2 particles with an amorphous structure were formed and distributed evenly on the parent cathode, without severe agglomeration. Electrochemical measurements at ambient temperature revealed that the MnO2-coated LiMn2O4 electrode exhibited superior rate capability as compared to the pristine LiMn2O4 electrode. Based on the capacity at low currents, the surface-modified electrode delivered 62% capacity, whereas the pristine LiMn2O4 electrode maintained 8% capacity during fast discharging for 3min at 20 C-rate. Surface coating with nano-MnO2 enhanced the electrochemical properties such as storage characteristics, particularly at elevated temperatures. X-ray photoelectron spectroscopy data showed that the improved performance of the coated electrode was mainly because of the suppressed side reaction between the cathode and the electrolyte.
In this paper, we illustrate that composite views about democracy vary significantly within and across national populations. Using World Values Survey data, we use latent class analysis to demonstrate that composite views of democracy display only modest consensus across country contexts. Although the features of procedural democracy are widely viewed as a cornerstone of democracy, their perceived importance and the way that they interact with substantive features varies considerably across and within democratic countries. These findings encourage caution when analyzing cross-national mass opinion about democracy. In particular, latent variable modeling using pooled survey data should pay careful attention to the unique permutations that democracy takes in the minds of citizens.
Oxygen reduction reaction (ORR) on Pt microelectrode was used for developing a micro pH sensor for scanning electrochemical microscopy (SECM) study in this work. When the potential of Pt microelectrode was held constant in ORR region, the ORR current (cathodic current) increased with decreasing solution pH and vice versa. The response time of the ORR current to pH changes was measured to be ca. 30ms which implies that the pH response is fast enough for monitoring the temporal pH changes. Furthermore, a fine linear relationship was found to exist between the half wave potential of ORR (E 1/2) and the solution pH value, and the slope is −46mV/pH. The Pt micro pH sensor was located 1μm above the LaNi5−x Al x (x =0, 0.3) substrate electrode surface in pH=9 KOH solution to perform the tip–substrate voltammetry of SECM. In tip voltammogram, the ORR tip current qualitatively reflects the transit solution pH changes during LaNi5−x Al x discharge reaction. Also, the minimum values of the solution pH near LaNi5 and LaNi4.7Al0.3 surface during the discharge reaction were quantitatively detected; they were 7.17 and 7.57, respectively. The result indicates that Al partial substitution for Ni degrades the maximum discharge ability of the alloy and decreases the hydrogen diffusion coefficient in alloy bulk.
Oxygen-deficient Li2MnO3−x (0 < x < 0.19) have been directly synthesized from lithium-rich manganese oxide, Li2MnO3, using metal hydrides (CaH2 and LiH) as reducing agents at reaction temperatures of 255–265 °C. The structure of the reduced phase determined by X-ray diffraction experiments has oxygen vacancies in the layered structure, causing slightly larger lattice parameters than the stoichiometric Li2MnO3. Reversible oxygen insertion and extraction from the deficient structure observed by the TG measurements suggests fast oxygen diffusion in the layered rock-salt structure. The oxygen-deficient phase shows extremely large 1st charge and discharge capacities of 388 and 305 mAh g−1, respectively.
The electrocatalysis of the hydroquinone oxidation at polyaniline-modified electrodes has been studied using cyclic voltammetry and the rotating disc electrode. A considerable increase of the exchange current density by two orders of magnitude was observed with freshly prepared films. Upon aging of the polyaniline film the effect showed a slight decrease.
Sn anode in rechargeable lithium ion batteries (LIBs) is currently being intensely investigated due to high reversible capacity and energy density as compared to the commercialized graphite anode. However, large volume change upon cycling causes poor cyclic performance, which prevents the practical application of Sn anode in LIBs. In this study, the nanosized M x Sn (M=Ni, Fe, and Cr) alloys were encapsulated in amorphous carbon nanotubes (ACNTs) creating hybrid anode heterostructures. The structure of the hybrid anodes was confirmed by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and high angle dark field scanning transmission electron microscope (HAADF-STEM), and demonstrated that Ni3Sn4, FeSn2, and Cr2Sn3 alloys exist in the hybrid anodes as both nanowires and nanoparticles. The galvanostatic cycling originating from over 330 charge–discharge cycles indicated that encapsulation of Ni3Sn4, FeSn2, and Cr2Sn3 into ACNTs results in surprisingly excellent cycling performance, high rate capability, and increased initial coulombic efficiency (81.4%). Ex situ HAADF-STEM images of anodes after cycles showed that one-dimensional ACNTs as well as electrochemically inactive phase M (Ni, Fe, and Cr) in M x Sn function as good matrices, offering “buffer zone” to effectively accommodate the mechanical stress induced by Sn anode expansion and shrinkage. Importantly, ACNTs enable electrical contact of Sn nanoparticles with the current collectors. Therefore, our design can significantly overcome electrochemical degradation of anodes with large volume change, resulting in increased LIB performance.
To investigate how heat development in the pulp chamber and coronal surface of natural teeth with and without cusps subjected to irradiance using light-emitting diode (LED)–light-curing units (LCUs) is associated with (i) irradiance, (ii) time, (iii) distance, and (iv) radiant exposure.
Accumulating evidence suggests that noradrenergic and serotonergic drugs are equally effective in ameliorating the depressive symptoms of major depression. Major depression is associated also with memory impairments, but the comparative effects of the antidepressant drugs on memory are not clear. We previously found that serotonergic neurotransmission is of particular importance for some aspects of episodic memory. We set out to test whether treatment with the selective serotonergic drug Fluoxetine (Prozac) would be advantageous in this respect over treatment with the selective noradrenergic tricyclic antidepressant drug Desipramine (Deprexan). Seventeen patients with major depressive episode, randomly assigned for treatment with either Fluoxetine (n=8) or Desipramine (n=9), were assessed for their clinical situation and for memory performance at the beginning of treatment, after 3 weeks, and after 6 weeks of pharmacological treatment. We found that although clinically both drugs were equally effective, the improvement of memory performance in the Fluoxetine-treated patients was significantly greater compared with that of the Desipramine-treated patients. The results support the role of serotonin in memory. More studies in larger samples of patients are required, but it may be that in cases where memory impairment is a major symptom, it would be beneficial to consider serotonergic antidepressant drugs for treatment. Furthermore, in cases where, for various reasons, the treatment of choice is noradrenergic, it may be worthwhile to consider a supplementary serotonergic drug to improve memory deficits.
Sulfur cathodes have attracted much attention recently because of their high energy density and power density. However, sulfur possesses very poor electrical conductivity, and lithium polysulfides, resulting from the lithiation of sulfur, are prone to dissolving into electrolytes, which leads to the loss of active materials and poor cyclic performance of the sulfur cathodes. Here we report an MnO2-graphene oxide (GO) double-shelled sulfur (S@MnO2@GO) with improved rate capability and cyclic performance, in which we propose a new reaction using sulfur-reducing KMnO4 to produce MnO2 that covers the surface of the excess sulfur in situ. The resulting MnO2 with honeycomb-like morphology provides excellent voids for storing polysulfides. The outermost GO was assembled to block the open pores of MnO2, thereby minimizing the opportunity for polysulfides to leach into the electrolytes. The GO significantly improved the electrical conductivity of the sulfur cathode, and the S@MnO2@GO exhibited excellent rate capability and long cycle life.
Transition metal oxalate materials have shown huge competitive advantages for applications in supercapacitors. Herein, nanostructured cobalt oxalate supported on cobalt foils has been facilely fabricated by anodization, and could directly serve as additive/binder-free electrodes for supercapacitors. The as-prepared cobalt oxalate electrodes present superior specific capacitance of 1269 F g−1 at the current density of 6 A g−1 in the galvanostatic charge/discharge test. Moreover, the retained capacitance is as high as 87.2% as the current density increases from 6 A g−1 to 30 A g−1. More importantly, the specific capacitance of cobalt oxalate retains 91.9% even after super-long cycling of 100,000 cycles. In addition, an asymmetric supercapacitor assembled with cobalt oxalate (positive electrode) and activated carbon (negative electrode) demonstrates excellent capacitive performance with high energy density and power density.
Nonaqueous gel electrolytes based on chitosan and 1-ethyl-3-methylimidazolim tetrafluoroborate (Chi/EMImBF4) are prepared for electric double-layer capacitors (EDLCs). The transparent colorless gel sheet has the high levels of mechanical strength and ionic liquid retention required in EDLC cells. Charge–discharge measurements revealed that a model EDLC cell with a chitosan gel exhibits high discharge capacitance although a gel-state electrolyte was used, indicating that the high affinity of chitosan for the activated carbon electrode decreases the electrode–electrolyte interfacial resistance. A test cell with Chi/EMImBF4 maintained a Coulombic efficiency of more than 99.9% during 5000 cycles.
The electrochemical lithium insertion process has been studied in the family of monophosphate tungsten bronzes (PO2)4(WO3)2m , where m =4 and 6. Structural changes in the pristine oxides were followed as lithium insertion proceeded. Through potentiostatic intermittent technique, the different processes which take place in the cathode during the discharge of the cell were analysed. The nature of the bronzes Li x (PO2)4(WO3)2m formed was determined by in situ X-ray diffraction experiments. These results have allowed establishment of a correlation with the reversible/irreversible processes detected during the electrochemical lithium insertion. Measurements of resistivity showed that upon lithium insertion, the metallic pristine oxides become insulating.
Highly-ordered mesoporous spinel ZnCo2O4 (HOM-ZnCo2O4) with controlled morphology, high surface area and narrow pore size distribution is prepared through a facile infiltration route with molecular sieve SBA-15 as templates for the first time. At the same time, nanostructured porous spherical spinel ZnCo2O4 (NPS-ZnCo2O4) framework is also synthesized using silicon spheres as templates. HOM-ZnCo2O4 is revealed to have a highly ordered mesoporous structure with a pore diameter of ∼4nm and a high surface area of 112.0m2 g−1, while NPS-ZnCo2O4 is a framework containing 3D connected pores with a diameter of ∼100nm and surface area of 88.4m2 g−1. As the anode material, HOM-ZnCo2O4 displays a high reversible specific capacity up to 1623mAhg−1, ∼300mAhg−1 larger than NPS-ZnCo2O4 (1286mAhg−1), at a current density of 2.0 Ag−1. When applying a high current density of 8.0Ag−1, the capacity of HOM-ZnCo2O4 still remains at a high level of 1470mAhg−1, but NPS-ZnCo2O4 undergoes a severe degradation to 751mAhg−1. The large specific surface area contributes much to the better rate performance of the former because it provides a larger cross section for Li+ flux. Also, the small pore size may be more in favor of maintaining the structural stability of porous spinel material than the large one. Aside from its nanostructured characteristics, an inner atomic synergistic effect within the cubic lattices may account for the superior electrochemical performance of HOM-ZnCo2O4. HOM-ZnCo2O4 that exhibits high capacities and well stability is a kind of competitive anode materials and highly-ordered mesoporous structure is superior in electrode design.
Negation, conjunction, and disjunction are major building blocks in the formation of concepts. This article presents a new model-based theory of these Boolean components. It predicts that individuals simplify the models of instances of concepts. Evidence corroborates the theory and challenges alternative accounts, such as those based on minimal descriptions, algebraic complexity, or structural invariance. A computer program implementing the theory yields more accurate predictions than these rival accounts. Two experiments showed that the numbers of models of a Boolean concept predict the difficulty of formulating a description of it. As mental models may also underlie deductive reasoning, the present theory integrates two hitherto separate areas of investigation.
Several clinical measures of sensory and motor function are used alongside patient-rated questionnaires to assess outcomes of carpal tunnel decompression. However there is a lack of evidence regarding which clinical tests are most responsive to clinically important change over time.
Summary The prevention of ischaemia and the adequate restitution of blood flow to ischaemic tissue are pivotal to halt the progression of cellular injury associated with decreased oxygen and nutrient supply. Accordingly, the search for novel strategies which aim at preventing ischaemia-reperfusion-induced tissue damage is still of major interest in flap surgery. Preconditioning represents an elegant approach to render the tissue more resistant against deleterious ischaemic insults. For many decades, ‘surgical delay’ has been the standard method of tissue preconditioning. During the last 10 years, ischaemic preconditioning was added to the repertoire of plastic surgeons to protect flaps from ischaemic necrosis. The invasiveness and expenditure of time of these procedures, however, have always been major drawbacks, hindering a wide distribution in clinical practice. Consequently, the motivation has all along been to further refine and simplify protective strategies. Recent experimental studies have now shown that efficient protection from ischaemic necrosis can also be achieved by remote preconditioning or pretreatment with chemical agents and growth factors, which mimic the action of surgical delay and ischaemic preconditioning. In addition, the local application of unspecific stressors, including both heating and cooling, have been shown to effectively improve flap microcirculation and, thus, tissue survival. In view of successful translational research, it is now time that the efficacy of these novel preconditioning procedures is proven in prospective randomised clinical trials.
TEMPO oxidized cellulose nanofibrils (TOCNF) were used as binder material to prepare bendable Li4Ti5O12 (LTO) electrodes. Carbon fiber (CF) layers were integrated as current collectors to enhance the mechanical properties and to increase the specific energy of the electrodes. These electrodes combined with CF current collectors (LTO/CF) show good electrochemical properties and are flexible, sustainable, mechanical and chemical stable, lightweight and produced by a water-based easy filtration process. An increase of the active material weight (LTO) from around 19% to 71% of the electrode and current collector combined weight is demonstrated with CF compared with a copper current collector. Additionally, preparation of the current collector material is non-expensive, quick and easy compared to that of carbon nanotube or graphene. To test the flexible battery application, 4000 times repeated bending was carried out on both the LTO electrodes and the LTO/CF electrodes. This had no significant effect on the morphology, mechanical and electrochemical properties of neither the LTO nor the LTO/CF electrodes. Addition of the CF layer improves the mechanical properties and specific capacity of the LTO-electrode. A thicker LTO electrode with only 2wt% TOCNF is demonstrated which is promising for thicker electrodes with high energy density. A full cell was assembled with the LTO/CF as negative electrode and LiFePO4 (LFP)/CF as positive, which exhibited a stable cycling performance and good energy density.
The mixed transition-metal layered compound, LiNi0.5Mn0.3Co0.2O2 (NMC532), is a promising high-energy cathode material. However, the required high-voltage (>4.3 V) cycling is accompanied by a rapid capacity fade associated with a complex redox mechanism that has not been clarified. Here we report soft x-ray absorption spectroscopy of NMC532 electrodes, both pristine and those charged to 4.2, 4.35, or 4.5 V in graphite/NMC532 cells. A quantitative sXAS analysis shows that about 20% of the nickel exists as Ni4+ in the as-synthesized NMC532. The Ni redox reaction contributes only to the experimental capacity obtained below 4.2 V, while Co redox reactions take place throughout the entire electrochemical cycling up to 4.5 V. In contrast to the changing ratio of the well-defined Ni2+, Ni3+ and Ni4+ ions, Co always displays ill-defined intermediate valence states in the charged NMC532 electrodes. This indicates an itinerant electron system in NMC electrodes related to the improved rate performance through Co doping. Additionally, about 20% of Ni2+ is found on the electrode surface at the high potential, which suggests that the electrode surface has either gone through surface reconstruction or reacted with the electrolyte at high voltage.
Recently, intelligent transportation systems (ITSs) have emerged. These systems can improve traditional transportation systems and provide traffic information to travelers. In the area of transportation, wireless sensor networks (WSNs) can replace the existing wired sensors and expensive traffic monitoring systems to mitigate the time and costs of installing such systems. However, accurate and on-time traffic information delivery is a major challenge, considering the energy constraints of sensor nodes. In this paper, we propose a two-tier architecture that includes a network of mobile objects (vehicles) in the upper layer and a hierarchical WSN in the bottom layer. Using this approach, a portion of loads on the low-power static sensor nodes can be transferred to mobile objects, such as powerful mobile devices. Moreover, to provide accurate and timely traffic information, a QoS-aware link cost function has been proposed and used for data transmission between the static sensor nodes. In addition, due to the mobility of the objects and the probability of losing packets in the mobile object tier, a reliable data forwarding mechanism has been proposed for this tier. In this mechanism, data packets are forwarded to the neighbors, which enhance the probability of the packets’ being received. The performance evaluation results indicate the effectiveness of the proposed architecture and data reporting mechanism for use in ITS applications.
The control of the growth of a Pb-based alloy grid is very important for extending the life of a lead-acid battery. In this study, the creep behavior of pure Pb was investigated in air, in a highly concentrated H2SO4 solution, and in a highly concentrated H2SO4 solution with the intermittent electrifying to the specimen electrode, which simulated the discharge–charge process of the lead-acid battery, in order to obtain the fundamental knowledge about the growth of the Pb-based alloy grid. The growth or the creep of pure Pb in the stress range of 4.0–6.0MPa was advanced by a dislocation creep mechanism. The creep rate in a 4.5kmolm−3 H2SO4 solution was also accelerated by the electrifying to the electrode. This suggests that the acceleration of the creep rate is closely related to the release of dislocations near the specimen surface by the electrifying.
The magnetic nature of lithium insertion materials of LiNi1−x Co x O2 (x =0, 1/4, 1/2, 3/4, and 1) were investigated by means of positive muon-spin rotation/relaxation (μ+SR) spectroscopy combined with X-ray diffraction (XRD) analyses and susceptibility measurements. Zero field μ+SR spectra for all the samples below 300K were well fitted by a dynamic Kubo–Toyabe function, indicating the existence of randomly oriented magnetic moments even at 2K, i.e., disordered state. The field distribution width Δ due to magnetic Ni3+ ions decreases exponentially with increasing x, suggesting that the Co substitution is likely to simply dilute Ni moments. This also supports that cobalt and nickel ions are homogeneously distributed in a solid matrix even in a muon-scale (microscopically), which is consistent with the results of macroscopic measurements.
We report on the structure and lithium ion transport properties of Li1.5Al0.5Ge1.5(PO4)3 (LAGP). This material is commercially available and is prepared as amorphous powders via a flame spray technique called Flash Creation Method (FCM). We crystallize and sinter the amorphous powders at different temperatures in order to alter grain size and grain boundary properties. The structure is then characterized by means of powder X-ray diffraction, atomic force microscopy, scanning electron microscopy and transmission electron microscopy with energy dispersive X-ray spectroscopy. AC impedance spectroscopy is used to study lithium ion transport. A maximum total conductivity of 2×10−4 Scm−1 at room temperature is found for a sample sintered at 750°C for 2h. In order to distinguish between grain and grain boundary contributions to the impedance spectra, equivalent circuit fits are carried out. The results are analysed in the framework of the classical brick layer model and of a finite-element approach taking into account non-ideal grain contacts. Our experimental results for the grain and grain boundary resistances are in good agreement with the predications of the finite-element approach.
Herein, a method has been described to rapidly obtain a semi-quantitative three-dimensional lithium distribution of a lithium-ion battery graphite anode using laser-induced breakdown spectroscopy (LIBS) measurements. LIBS measurements of the graphite anodes with a diameter of 10 mm were performed in an argon atmosphere of 1000 Pa until the depth of 150 μm using the Li emission line of 610.4 nm. The emission intensity was measured for the pitch of 500 μm in plane. Homogeneous and inhomogeneous lithium distributions were observed in the anodes after both charge and charge-discharge processes. The inhomogeneous lithium distribution after the charge process was attributed to the preferentially reacted area in the anode, while that after the charge-discharge process was likely related to the low desolvation reaction rate of lithium ions at the solid electrolyte interphase. These inhomogeneous lithium distributions were consistent with the results from the charge-discharge curves and the lithium ion transfer mechanism. Thus, it was proven that it is possible to acquire a three-dimensional lithium distribution of a graphite anode of a lithium-ion battery by LIBS measurements.
The carbon/electrolyte interface was characterized during galvanostatic cycling at different current densities by means of impedance spectroscopy, semi-in situ transmission microscopy and Fourier-transform infrared spectroscopy (FT–IR). These techniques, carried-out in an inert atmosphere, showed that the formation rate strongly influences both the chemical nature and thickness of this interface; its growth will be detailed using a rate corresponding to the intercalation of one lithium in 20h.