Process feasibility study in support of silicon material, task 1

Analyses of process system properties were continued for materials involved in the alternate processes under consideration for semiconductor silicon. Primary efforts centered on physical and thermodynamic property data for dichlorosilane. The following property data are reported for dichlorosilane which is involved in processing operations for solar cell grade silicon: critical temperature, critical pressure, critical volume, critical density, acentric factor, vapor pressure, heat of vaporization, gas heat capacity, liquid heat capacity and density. Work was initiated on the assembly of a system to prepare binary gas mixtures of known proportions and to measure the thermal conductivity of these mixtures between 30 and 350 C. The binary gas mixtures include silicon source material such as silanes and halogenated silanes which are used in the production of semiconductor silicon

Process feasibility study in support of silicon material task 1

Results for process system properties, chemical engineering and economic analyses of the new technologies and processes being developed for the production of lower cost silicon for solar cells are presented. Analyses of process system properties are important for chemical materials involved in the several processes under consideration for semiconductor and solar cell grade silicon production. Major physical, thermodynamic and transport property data are reported for silicon source and processing chemical materials

Ammonia emissions from deciduous forest after leaf fall

The understanding of biochemical feedback mechanisms in the climate system is lacking knowledge in relation to bi-directional ammonia (NH3) exchange between natural ecosystems and the atmosphere. We therefore study the atmospheric NH3 fluxes during a 25-day period during autumn 2010 (21 October to 15 November) for the Danish beech forest Lille Bøgeskov to address the hypothesis that NH3 emissions occur from deciduous forests in relation to leaf fall. This is accomplished by using observations of vegetation status, NH3 fluxes and model calculations. Vegetation status was observed using plant area index (PAI) and leaf area index (LAI). NH3 fluxes were measured using the relaxed eddy accumulation (REA) method. The REA-based NH3 concentrations were compared to NH3 denuder measurements. Model calculations of the atmospheric NH3 concentration were obtained with the Danish Ammonia MOdelling System (DAMOS). The relative contribution from the forest components to the atmospheric NH3 flux was assessed using a simple two-layer bi-directional canopy compensation point model. A total of 57.7% of the fluxes measured showed emission and 19.5% showed deposition. A clear tendency of the flux going from deposition of −0.25 ± 0.30 μg NH3-N m−2 s−1 to emission of up to 0.67 ± 0.28 μg NH3-N m−2 s−1 throughout the measurement period was found. In the leaf fall period (23 October to 8 November), an increase in the atmospheric NH3 concentrations was related to the increasing forest NH3 flux. Following leaf fall, the magnitude and temporal structure of the measured NH3 emission fluxes could be adequately reproduced with the bi-directional resistance model; it suggested the forest ground layer (soil and litter) to be the main contributing component to the NH3 emissions. The modelled concentration from DAMOS fits well the measured concentrations before leaf fall, but during and after leaf fall, the modelled concentrations are too low. The results indicate that the missing contribution to atmospheric NH3 concentration from vegetative surfaces related to leaf fall are of a relatively large magnitude. We therefore conclude that emissions from deciduous forests are important to include in model calculations of atmospheric NH3 for forest ecosystems. Finally, diurnal variations in the measured NH3 concentrations were related to meteorological conditions, forest phenology and the spatial distribution of local anthropogenic NH3 sources. This suggests that an accurate description of ammonia fluxes over forest ecosystems requires a dynamic description of atmospheric and vegetation processes

Process feasibility study in support of silicon material task 1

Initial results for gas thermal conductivity of silicon tetrafluoride and trichlorosilane are reported in respective temperature ranges of 25 to 400 C and 50 to 400 C. For chemical engineering analyses, the preliminary process design for the original silane process of Union Carbide was completed for Cases A and B, Regular and Minimum Process Storage. Included are raw material usage, utility requirements, major process equipment lists, and production labor requirements. Because of the large differences in surge tankage between major unit operations the fixed capital investment varied from $19,094,000 to$11,138,000 for Cases A and B, respectively. For the silane process the original flowsheet was revised for a more optimum arrangement of major equipment, raw materials and operating conditions. The initial issue of the revised flowsheet (Case C) for the silane process indicated favorable cost benefits over the original scheme

Did Covid-19 lead to an increase in hate crime against Chinese people in London?

We examine whether Covid-19, which is widely believed to have originated in China, negatively affected the environment for Chinese people in London leading to an increase in hate crimes towards this group relative to others. With data from the Metropolitan Police for the whole of the Metropolitan area of London we use a difference-in-differences approach to examine what happened to hate crimes against Chinese people in London in the months before (Oct-Dec 2019) and the months after the Covid-19 pandemic (Jan-Mar 2020) relative to other ethnic groups, to other crimes and to other time periods. Our methodology utilises the fact that Covid-19 came as an unexpected shock, which very quickly changed the environment for crime, and did so differentially across ethnicities. We argue that this shock is likely to negatively impact on attitudes and behaviours towards Chinese people, but have no effect on other ethnicities. Our results show that in the months after Covid-19 there was an increase in hate crimes against Chinese people, but this increase was not seen amongst the other ethnic groups, other non-hate crimes, nor in any other time period. This leads us to conclude that Covid-19 lead to an increase in hate crimes against Chinese people in London. That Covid-19 changed behaviour towards Chinese people highlights an intrinsic link between Covid-19 and racism. Unfortunately, the rise in hate crime that we identify adds to a growing list of ways in which ethnic minority groups disproportionately suffered, and continue to do so, during the pandemic

Did the first Covid-19 national lockdown lead to an increase in domestic abuse in London?

On March 23rd 2020, the UK, following close behind a number of other countries went into its first national lockdown in a bid to stop the spread of Covid-19. Boris Johnson told people to stay at home and save lives. But what happens when home isn’t safe? This paper uses data from the Metropolitan Police to examine the impact of the first lockdown on domestic abuse in the 32 boroughs of the London Metropolitan area. Using a before and after approach, and controlling for other factors, we show that domestic abuse crimes rose during lockdown. We find this increase is greater for some crimes and populations than others and is consistent across the whole lockdown period. Once lockdown restrictions are eased, rates decline but remain slightly higher than prior to lockdown up to 3 months later