3D Simulation of the Effects of Surface Defects on Field Emitted Electrons

The ev­er-grow­ing de­mand for high­er beam en­er­gies has dra­mat­i­cal­ly in­creased the risk of RF break­down, lim­it­ing the max­i­mum achiev­able ac­cel­er­at­ing gra­di­ent. Field emis­sion is the most fre­quent­ly en­coun­tered RF break­down where it oc­curs at re­gions of lo­cal­ly en­hanced elec­tric field. Elec­trons ac­cel­er­at­ed across the cav­i­ty as they tun­nel through the sur­face in the pres­ence of mi­cro­scop­ic de­fects. Upon Im­pact, most of the ki­net­ic en­er­gy is con­vert­ed into heat and stress. This can in­flict ir­re­versible dam­age to the sur­face, cre­at­ing ad­di­tion­al field emis­sion sites. This work aims to in­ves­ti­gate, through sim­u­la­tion, the physics in­volved dur­ing both emis­sion and im­pact of elec­trons. A newly de­vel­oped 3D field model of an 805 MHz cav­i­ty is gen­er­at­ed by COM­SOL Mul­ti­physics. Elec­tron track­ing is per­formed using a Mat­lab based code, cal­cu­lat­ing the rel­e­vant pa­ram­e­ters need­ed by em­ploy­ing fourth Order Runge Kutta in­te­gra­tion. By study­ing such be­haviours in 3D, it is pos­si­ble to iden­ti­fy how the cav­i­ty sur­face can alter the local RF field and lead to break­down and sub­se­quent dam­ages. The ul­ti­mate aim is to in­tro­duce new sur­face stan­dards to en­sure bet­ter cav­i­ty per­for­mance

THE EFFECTS OF FIELD EMITTED ELECTRONS ON RF SURFACE

The ever-growing demand for higher RF gradients has considerably increased the risk of breakdown in accelerating structures. Field emission is the most common form of RF breakdown that generates free electrons capable of inflicting irreversible damages on the RF surface. This paper presents a systematic experimental and simulation programme to understand possible sources and their influence on RF cavity operatio

Psychometric assessment of beck scale for suicidal ideation (BSSI) in general population in Tehran

Background: Beck Scale for Suicidal Ideation (BSSI) is a widely used instrument to assess suicidality. However, there is only limited information about the psychometric characteristics of BSSI in the Persian language. In this study, we investigated the validity, reliability and factor structure of the BSSI in the general population of Tehran. Methods: Initially, 900 questionnaire packages were distributed to the general population of Tehran (response rate: 59 percent), using cluster random sampling method. The questionnaire package consisted of a demographic questionnaire, the Persian translation of the BSSI, Symptom checklist-90- Revised (SCL-90-R), Beck Hopelessness Inventory (BHI) and Philips Social Support Appraisal Scale. Internal consistency and correlations of the BSSI scores with other constructs were investigated. Factor analysis was done using principal component method. Results: The Cronbach's alpha coefficients of the screening part and the whole scale were satisfactory (>0.8). The scores of both the screening part and the total scale in individuals who experienced suicidal attempt were higher than others. Both the screening part and the total scale had a positive correlation with depression and Global Severity Index in SCL-90-R, and a negative correlation with social support. The scores of the screening part had a positive correlation with anxiety, psychoticism, hostility and hopelessness as well. The screening part consisted of a single factor which explains 60 of the total variance. Conclusion: The Persian translation of the BSSI has desirable psychometric properties in research setting. However, the clinical usage of the scale remains to be explored, and the factor structure of the whole questionnaire should be assessed in a clinical sample

Artificial leaf device for hydrogen generation from immobilised C. reinhardtii microalgae

We developed a fully biomimetic leaf-like device for hydrogen production which allows incorporated fabric-immobilised microalgae culture to be simultaneously hydrated with media and harvested from the produced hydrogen in a continuous flow regime without the need to replace the algal culture. Our leaf device produces hydrogen by direct photolysis of water resulting from redirecting the photosynthetic pathways in immobilised microalgae due to the lack of oxygen. In contrast to the many other reports in the literature on batch photobioreactors producing hydrogen from suspension culture of microalgae, we present the first report where this is done in a continuous manner from a fabric-immobilised microalgae culture. The reported artificial leaf device maximises the sunlight energy utilisation per gram of algae and can be upscaled cheaply and easily to cover large areas. We compared the production of hydrogen from both immobilised and suspended cultures of C. reinhardtii microalgae under sulphur, phosphorus and oxygen deprived conditions. The viability and potential of this approach is clearly demonstrated. Even though this is a first prototype, the hydrogen yield of our artificial leaf device is twenty times higher per gram of algae than in previously the reported batch reactors. Such leaf-like devices could potentially be made from flexible plastic sheets and installed on roofs and other sun-exposed surfaces that are inaccessible by photovoltaic cells. The ability to continuously produce inexpensive hydrogen by positioning inexpensive sheets onto any surface could have an enormous importance in the field of biofuels. The proposed new concept can provide a cleaner and very inexpensive way of bio-hydrogen generation by flexible sheet-like devices

An Empirical Growth Model for Major Oil Exporters

This paper develops a long-run growth model for a major oil exporting economy and derives conditions under which oil revenues are likely to have a lasting impact. This approach contrasts with the standard literature on the "Dutch disease" and the "resource curse", which primarily focuses on short-run implications of a temporary resource discovery. Under certain regularity conditions and assuming a Cobb-Douglas production function, it is shown that (log) oil exports enter the long-run output equation with a coefficient equal to the share of capital (). The long-run theory is tested using quarterly data on nine major oil economies, six of which are current members of OPEC (Iran, Kuwait, Libya, Nigeria, Saudi Arabia, and Venezuela), plus Indonesia which is a former member, and Mexico and Norway, which are members of the OECD. Overall, the test results support the long-run theory. The existence of long-run relations between real output, foreign output and real oil income is established for six of the nine economies considered. The exceptions, Mexico and Norway, do not possess sufficient oil reserves for oil income to have lasting impacts on their economies. At their current production rates, the proven oil reserves of Mexico and Norway are expected to last 9 and 10 years respectively, as compared to reserve-production ratios of OPEC members, which lie in the range of 45 to 125 years. For Indonesia, whose share of oil income in GDP has been declining steadily over the past three decades, the theory suggests that the effect of oil income on the economy's steady state growth rate will vanish eventually, and this is indeed confirmed by the results. Sensible estimates of a are also obtained across the six economies with long-run output equations, and impulse responses are provided for the effects of shocks to oil income and foreign output in these economies

Linking a simulated annealing based optimization model with PHT3D simulation model for chemically reactuve transport processes to optimally characterize unknown contaminant sources in a former mine site in Australia

Historical mining activities often lead to continuing wide spread contaminants in both groundwater and surface water in previously operational mine site areas. The contamination may continue for many years after closing down the mining activities. The essential first step for sustainable management of groundwater and development of remediation strategies is the unknown contaminant source characterization. In a mining site, there are multiple species of contaminants involving complex geochemical processes. It is difficult to identify the potential sources and pathways incorporating the chemically reactive multiple species of contaminants making the source characterization process more challenging. To address this issue, a reactive transport simulation model PHT3D is linked to a Simulated Annealing based the optimum decision model. The numerical simulation model PHT3D is utilized for numerically simulating the reactive transport process involving multiple species in the former mine site area. The simulation results from the calibrated PHT3D model are illustrated, with and without incorporating the chemical reactions. These comparisons show the utility of using a reactive, geochemical transport process’ simulation model. Performance evaluation of the linked simulation optimization methodology is evaluated for a contamination scenario in a former mine site in Queensland, Australia. These performance evaluation results illustrate the applicability of linked simulation optimization model to identify the source characteristics while using PHT3D as a numerical reactive chemical species’ transport simulation model for the hydro-geochemically complex aquifer study area

Role of molecular architecture and temperature on extrusion melt flow instabilities of two industrial LLDPE and LDPE polyethylenes investigated by capillary rheology, high‐pressure sensitivity slit die and optical analysis

The characteristic time periodicity $\tau^{*}$ and the spatial characteristic wavelength ${\lambda}$ of extrusion flow instabilities of a linear and a branched commercial polyethylene (PE) are characterized via capillary rheology, optical analysis and modeled. The two investigated polyethylenes have the similar weight average molecular weight (Mw). The characteristic time periodicity $\tau^{*}$ is obtained and compared using three methods: (i) a highly sensitive pressure slit die, (ii) a new online optical analysis method based on the construction of a space–time diagrams, and (iii) an offline transmission polarization microscopy. In addition, the spatial characteristic wavelength ${\lambda}$ is quantified by offline transmission polarization microscopy. The characteristic time periodicity $\tau^{*}$ of the extrusion flow instabilities follows a power law behavior as a function of apparent shear rate to a power of −0.7 for both materials, $\tau$$^{*}{\propto^.\gamma}^{-0.7}_{app.}$. A qualitative model is used to predict the spatial characteristic wavelength of extrusion flow instabilities as well. It is found that the characteristic spatial wavelength ${\lambda}$ and the characteristic time periodicity $\tau^{*}$ have an Arrhenius temperature-dependent behavior

Role of molecular architecture and temperature on extrusion melt flow instabilities of two industrial LLDPE and LDPE polyethylenes investigated by capillary rheology, high-pressure sensitivity slit die and optical analysis

The characteristic time periodicity (Formula presented.) and the spatial characteristic wavelength (Formula presented.) of extrusion flow instabilities of a linear and a branched commercial polyethylene (PE) are characterized via capillary rheology, optical analysis and modeled. The two investigated polyethylenes have the similar weight average molecular weight (Mw). The characteristic time periodicity (Formula presented.) is obtained and compared using three methods: (i) a highly sensitive pressure slit die, (ii) a new online optical analysis method based on the construction of a space–time diagrams, and (iii) an offline transmission polarization microscopy. In addition, the spatial characteristic wavelength λ is quantified by offline transmission polarization microscopy. The characteristic time periodicity (Formula presented.) of the extrusion flow instabilities follows a power law behavior as a function of apparent shear rate to a power of −0.7 for both materials, (Formula presented.). A qualitative model is used to predict the spatial characteristic wavelength (Formula presented.) of extrusion flow instabilities as well. It is found that the characteristic spatial wavelength λ and the characteristic time periodicity (Formula presented.) have an Arrhenius temperature-dependent behavior

Managing user engagement in Virtual event platforms

Virtual platforms are considered as an innovative solution, and sometime a disruptive innovation, helping various industries to operate and interact with stakeholders and institutes to educate and inform users. Virtual conference and events have been on the rise and proved to be an effective solution in this unprecedent era. However, how the virtual event was received by users needs to be explored. Applying classical theories of user engagement, this paper aims to understand what has affected participant's level of engagement and attitude towards Virtual conferences over the last 18 months. A sample of 70 participants were recruited and two groups of antecedents of service provider and participants and their relationships with engagement and participants attitude is examined. Data analysis indicated that perceived conference informativeness and perceived service quality indicate 74% and 69% of the total variation in user engagement respectively and 82% and 77% of the total variation in participant's attitude towards virtual conferencing. This is a great insight and in contradiction to factors impacting engagement in a non-virtual environment