Theoretical study of superionic phase transition in Li2S

We have studied temperature-induced superionic phase transition in Li2S, which is one of the most promising Li-S battery cathode material. Concentration of ionic carriers at low and high temperature was evaluated from thermodynamics of defects (using density functional theory) and detailed balance condition (using ab initio molecular dynamics (AIMD)), respectively. Diffusion coefficients were also obtained using AIMD simulations. Calculated ionic conductivity shows that superionic phase transition occurs at T = 900 K, which is in agreement with reported experimental values. The superionic behavior of Li2S is found to be due to thermodynamic reason (i.e. a large concentration of disordered defects)

Effect of Ursodeoxycholic Acid on Pentylenetetrazole Kindling and Kindling Induced Memory Impairment in Rat

BACKGROUND AND OBJECTIVE: Epilepsy is one of the common diseases of the brain that about 30-40% of patients with epilepsy experience recurent attacks due to drug resistance. Recently, the beneficial effects of Ursodeoxycholic acid on brain disorders have been considered. The aim of this study was to evaluate the effect of Ursodeoxycholic acid(UDCA)on the Pentylenetetrazole (PTZ) induced kindling, and related learning and memory impairments on Morris water maze. METHODS: This experimental study was done on 32 male Winstar rats divided into 4 groups. The first(n=7)and the second(n=9)groups have received three injections of 0.5 ml NaCl or 50 mg/kg of UDCA respectively and third(n=7) and fourth(n=9) groups have received fifteen injections of 0.5 ml NaCl or 50 mg/kg of UDCA respectively. All injections were given intraperitoneally(ip)(every 48 hours). In all groups, chemical kindling were started after third injections. Twenty-four hour after the last injection, spatial memory was investigated in the Morris water maze. FINDING: Fifteen injections of UDCA significantly reduced the seizure stage from 3.5±0.17 to 3.08±0.11 and duration of stages five from 12.37±1.21 to 8.43±1.09 and increased time to reach the stage five seizures from 1021.65±72.07 to 1252.41±49.63 as compared to control group. However, three injections of UDCA have no effect on the kindling process. However, three time administration of UDCA significantly increased reference memory from 18.72±1.2 s to 26.11±1.8 s. CONCLUSION: Ursodeoxycholic acid inhibits chemical kindling and improves kindling induced memory impairment

First Principles Study of Li-based Battery Materials: Electronic Structure, Thermodynamics, and Kinetics

Recently, lithium(Li)-based batteries have attracted significant attention due to their applications in electric vehicles and many new kinds of portable electronic devices such as cell phones. However, such batteries still need more research and improvement in order to meet the market demands for low cost and high-rate performance. Lithium-sulfur (Li-S) batteries with their high theoretical energy density, and all-solid-state Li-ion batteries (ASSLB) with their increased safety and design flexibility are among the most promising energy-storage systems. The focus of current dissertation is set on the important materials in these two kinds of batteries. The common cathode materials for Li-S batteries are S8 or Li2S. Intermediate Li-polysulfides are also formed at the cathode during the charge/discharge process. Moreover, carbon-based materials are added to sulfur cathodes in order to increase their electronic conductivity. In Li-S batteries, the Li-polysulfides migrate through the electrolyte, and their reductions and oxidations on both electrodes result in excessive utilization of the active material and self discharging. To inhibit this process, traping of Li-polysulfides in the cathode has been proposed. Here, we have investigated the ability of graphene (pristine and defective) as part of sulfur cathode to trap the Li-polysulfides. To this end, binding energies and Gibbs free energies for adsorption process of Li2Sx onto the graphene are calculated using Density Functional Theory (DFT) with PBE-D2 method. To calculate the Gibbs free energies, vibrational and configurational entropies are evaluated. It is found that the interaction of the Li-polysulfides and graphene is mostly dominated by the dispersion interactions, and pristine as well as defective graphene cannot immobilize the Li-polysulfides. Although during the adsorption of Li2Sx on monovacant graphene, one S atom is chemically attached to the defect site, the resulting S-doped graphene cannot hinder the Li-polysulfide migration either. In the next step, Li2S, which is one of the promising cathode materials in Li-S batteries, has been investigated. Similar to S8 , Li2S has a low electronic conductivity. Moreover, Li-ion conductivity of Li2S at room temperature is low, but this crystal possesses a high ionic conductivity at high temperatures. Although many experiments have been performed to study the ionic conductivity of Li2S, it has not been studied theoretically so far. In this thesis, we have studied ionic conductivity of Li2S as well as the origin of its superionic phase transition which has been reported by experimentalists. To achieve this aim, we have applied DFT and ab initio molecular dynamics (AIMD). Through AIMD simulations at different temperatures, diffusion coefficients are evaluated. Additionally, concentration of the Li ions is calculated from thermodynamics of defects as well as using the detailed balance condition. Finally, the Li-ion conductivity is obtained for various temperatures which shows the superionic phase transition for temperatures above T = 900K, in good agreement with the experimental reports. In the case of ASSLBs, although the solid electrolyte has a high ionic conductivity and a high stability, such systems do not possess a high energy density compared to the conventional cells, which is due to a large interfacial resistance at electrolyte/electrode interface. Therefore, it is of crucial importance to know the atomic and electronic structures of these interfaces. In this work, an important electrolyte/cathode interface for ASSLBs, namely Li7La3Zr2O12 /LiCoO2, has been investigated. Although several experimental researches have synthesized and studied this interface, its complex structure makes it difficult to investigate theoretically. Here, for the first time, we have modeled and studied this interface using DFT (PBE+U method) by focusing on Li7La3Zr2O12(001)/LiCoO2(10-14). To consider the effect of lattice mismatch between the two surfaces, three models with different lattice parameters for the interface have been applied. Therefore, different magnitudes of biaxial compressive and tensile strains are applied on the interface. It is shown that during the interface optimization, a Li ion moves from the surface of LiCoO2 to Li7La3Zr2O12. This ion migration is accompanied by electron transfer in the same direction attempting to neutralize the system. The electron transfer also results in the formation of certain gap states at the interface. In the next step, the possibility of cation interchange (Co↔Zr or Co↔La) has been studied at the Li7La3Zr2O12(001)/LiCoO2(10-14) interface. By calculating the energy difference between interface with interchanged cations and pristine interface, it is found that this process is possible only under a large stress along the interface normal direction. In addition, to minimize the strain on such systems during the cation interchange, the bulk models of Li7La3Zr2O12 and LiCoO2 have been considered, and the full optimization has been carried out for these bulk structures. Moreover, to increase the accuracy, HSE06 hybrid functional has been applied. Comparing with pristine Li7La3Zr2O12 and LiCoO2 bulks, the structures with Co↔Zr or Co↔La cation interchange are unfavorable. As a result, these structures can only form under a large stress which is consistent with experimental observations, showing the cation interchange during the cathode annealing at high temperatures. In the case of Li-S batteries, our findings show that pristine and even vacant graphene in sulfur cathode do not have the ability to catch the Li-polysulfides. Therefore, another way to trap the Li-polysulfides should be proposed. According to the experimental results, doping of graphene by certain dopants such as nitrogen or phosphorus can immobilize the Li2Sx molecules, and improve the performance of sulfur cathode. This process should be studied theoretically in detail, similar to what we have done for pristine and defective graphene. In order to study the Li-ion conductivity, the approach that has been used in Li2S can be applied to model superionic phase transition in ionic crystals. In addition, at Li7La3Zr2O12(001)/LiCoO2(10-14) interface, our calculations enable us to have a better understanding of processes at such interfaces which will eventually lead to fabricate the more efficient ASSLB

Nuclear quantum effects in fullerene–fullerene aggregation in water

We studied the effects of the quantum delocalization in space of the hydrogen atoms of water in the aggregation process of two fullerene molecules. We considered a case using a purely repulsive water–fullerene interaction, as such a situation has shown that water-mediated effects play a key role in the aggregation process. This study becomes feasible, at a reduced computational price, by combining the path integral (PI) molecular dynamics (MD) method with a recently developed open-system MD technique. Specifically, only the mandatory solvation shell of the two fullerene molecules was considered at full quantum resolution, while the rest of the system was represented as a mean-field macroscopic reservoir of particles and energy. Our results showed that the quantum nature of the hydrogen atoms leads to a sizable difference in the curve of the free energy of aggregation; that is, that nuclear quantum effects play a relevant role

Path Integral Molecular Dynamics of Liquid Water in a Mean-Field Particle Reservoir

We present a simulation scheme for path integral simulation of molecular liquids where a small open region is embedded in a large reservoir of non interacting point-particles. The scheme is based on the latest development of the adaptive resolution technique AdResS and allows for the space-dependent change of molecular resolution from a path integral representation with 120 degrees of freedom to a point particle that does not interact with other molecules and vice versa. The method is applied to liquid water and implies a sizable gain regarding the request of computational resources compared to full path integral simulations. Given the role of water as universal solvent with a specific hydrogen bonding network, the path integral treatment of water molecules is important to describe the quantum effects of hydrogen atoms’ delocalization in space on the hydrogen bonding network. The method presented here implies feasible computational efforts compared to full path integral simulations of liquid water which, on large scales, are often prohibitive

Graph Theory

Graph Theory is a graphical representation of a set of vertices which are connected by edges and is basically suitable in computer science and mathematics to create structural models. This paper describes the basic terminology of graphs, different types and connectivity of graphs to lead new inventions and modifications in the existing environment for enhancement in these fields

First trimester determination of fetal gender by ultrasonographic measurement of anogenital distance: A cross-sectional study

Background: In some patients with a family history of the gender-linked disease, determination of the fetal gender in the first trimester of pregnancy is of importance. In X-linked recessive inherited diseases, only the male embryos are involved, while in some conditions, such as congenital adrenal hyperplasia, female embryos are affected; hence early determination of fetal gender is important. Objective: The aim of the current study was to predict the gender of the fetus based on the accurate measurement of the fetal anogenital distance (AGD) by ultrasound in the first trimester. Materials and Methods: To determine the AGD and crown-rump length in this cross-sectional study, 316 women with singleton pregnancies were exposed to ultrasonography. The results were then compared with definitive gender of the embryos after birth. Results: The best cut-off for 11 wk to 11 wk, 6 days of pregnancy was 4.5 mm, for 12 wk to 12 wk, 6 days was 4.9 mm, and for 13 wk to 13 wk, 6 days was 4.8 mm. Conclusion: AGD is helpful as an ultrasonographic marker that can determine fetal gender in the first trimester, especially after 12 wks. Key words: Sonography, Gender, Female, Male, Pregnancy, First trimester

The effectiveness of dolomite and Ni-catalyst mixtures for pure H 2 production by methane steam reforming via CO 2 capture

High hydrogen yields have been obtained continuously from steam reforming of methane coupled with simultaneous CO2 capture[1], at lower temperature (630oC) and pressure (1 atm) than those typical of traditional processes (800-900oC,15-30 atm), using calcined dolomite and a pulverized commercial Ni catalyst, in a single step. On the other hand, a pure CO2 stream is obtained by subsequent regeneration of the sorbent, which could be stored. A bubbling fluidized bed contained in a quartz vessel was operated batchwise. First, the durability of a dolomite in multi-cycle CO2 sorption/desorption runs has been investigated: a remarkable reduction of dolomite activity is observed after the first calcination, but substantially stable activity was conserved up to the fifth cycle. Then the performance of sorption enhanced catalytic steam reforming of methane to pure hydrogen has been evaluated. Two well distinct operation regimes have been found: before dolomite saturation, H2 concentration in the dry product gas remained stable at 94-96%, and CO2 was completely converted into calcium carbonate; after a short breakthrough period, concentration of H2 at the exit of the reactor reduced its value that became approximately equal to the equilibrium value expected for methane reforming and water gas shift reactions