Capacity estimation and code design principles for continuous phase modulation (CPM)

Continuous Phase Modulation is a popular digital modulation scheme for systems which have tight spectral efficiency and Peak-to-Average ratio (PAR) constraints. In this thesis we propose a method of estimating the capacity for a Continuous Phase Modulation (CPM) system and also describe techniques for design of codes for this system. We note that the CPM modulator can be decomposed into a trellis code followed by a memoryless modulator. This decomposition enables us to perform iterative demodulation of the signal and improve the performance of the system. Thus we have the option of either performing iterative demodulation, where the channel decoder and the demodulator are invoked in an iterative fashion, or a non-iterative demodulation, where the demodulation is performed only once followed by the decoding of the message. We highlight the recent results in the estimation of capacity for channels with memory and apply it to a CPM system. We estimate two different types of capacity of the CPM system over an Additive White Gaussian Noise (AWGN). The first capacity assumes that optimum demodulation and decoding is done, and the second one assumes that the demodulation is done only once. Having obtained the capacity of the system we try to approach this capacity by designing outer codes matched to the CPM system. We utilized LDPC codes, since they can be designed to perform very close to capacity limit of the system. The design complexity for LDPC codes can be reduced by assuming that the input to the decoder is Gaussian distributed. We explore three different ways of approximating the CPM demodulator output to a Gaussian distribution and use it to design LDPC codes for a Bit Interleaved Coded Modulation (BICM) system. Finally we describe the design of Multi Level Codes (MLC) for CPM systems using the capacity matching rule

Empirical Evaluation of Pre-trained Transformers for Human-Level NLP: The Role of Sample Size and Dimensionality

In human-level NLP tasks, such as predicting mental health, personality, or demographics, the number of observations is often smaller than the standard 768+ hidden state sizes of each layer within modern transformer-based language models, limiting the ability to effectively leverage transformers. Here, we provide a systematic study on the role of dimension reduction methods (principal components analysis, factorization techniques, or multi-layer auto-encoders) as well as the dimensionality of embedding vectors and sample sizes as a function of predictive performance. We first find that fine-tuning large models with a limited amount of data pose a significant difficulty which can be overcome with a pre-trained dimension reduction regime. RoBERTa consistently achieves top performance in human-level tasks, with PCA giving benefit over other reduction methods in better handling users that write longer texts. Finally, we observe that a majority of the tasks achieve results comparable to the best performance with just $\frac{1}{12}$ of the embedding dimensions.Comment: 2021 Annual Conference of the North American Chapter of the Association for Computational Linguistics (NAACL-HLT

Ursolic acid inhibits colistin efflux and curtails colistin resistant Enterobacteriaceae

Abstract Colistin resistance in Enterobacteriaceae especially Klebsiella pneumoniae and Escherichia coli is driving the evolution of pan drug resistant strains. Screening a library of 13 plant nutraceuticals led to the identification of acetyl shikonin and ursolic acid, which exhibited synergy with colistin against extremely drug resistant (XDR) clinical strains of E. coli (U3790) and K. pneumoniae (BC936). Ursolic acid caused a significant colistin MIC reversal of 16-fold in U3790 and 4-fold in BC936 strains. Ursolic acid also potentiated the bactericidal effect of colistin against both U3790 and BC936 by causing ~ 4 to 4.5 log fold decline in CFU of both clinical isolates in a time kill assay. At 2× minimum effective concentration, ursolic acid was non-toxic to zebrafish as evidenced by brain and liver enzyme profiles and by histopathology studies. In combination with colistin, ursolic acid reduced bacterial bioburden of U3790/BC936 by 1–1.58 log fold from the infected muscle tissue of zebrafish. Mechanistic explorations via studies on real time efflux, membrane potential and intracellular accumulation of dansyl chloride tagged colistin revealed that colistin efflux is inhibited by ursolic acid. In addition, ursolic acid also enhanced outer membrane permeability which probably facilitates colistin’s attack on outer and inner membranes. Our study shows that ursolic acid synergizes with colistin by inhibiting colistin efflux in Enterobacteriaceae that helps to curtail colistin resistant Enterobacteriaceae.https://deepblue.lib.umich.edu/bitstream/2027.42/148135/1/13568_2019_Article_750.pd

Global, regional, and national burden of disorders affecting the nervous system, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BackgroundDisorders affecting the nervous system are diverse and include neurodevelopmental disorders, late-life neurodegeneration, and newly emergent conditions, such as cognitive impairment following COVID-19. Previous publications from the Global Burden of Disease, Injuries, and Risk Factor Study estimated the burden of 15 neurological conditions in 2015 and 2016, but these analyses did not include neurodevelopmental disorders, as defined by the International Classification of Diseases (ICD)-11, or a subset of cases of congenital, neonatal, and infectious conditions that cause neurological damage. Here, we estimate nervous system health loss caused by 37 unique conditions and their associated risk factors globally, regionally, and nationally from 1990 to 2021.MethodsWe estimated mortality, prevalence, years lived with disability (YLDs), years of life lost (YLLs), and disability-adjusted life-years (DALYs), with corresponding 95% uncertainty intervals (UIs), by age and sex in 204 countries and territories, from 1990 to 2021. We included morbidity and deaths due to neurological conditions, for which health loss is directly due to damage to the CNS or peripheral nervous system. We also isolated neurological health loss from conditions for which nervous system morbidity is a consequence, but not the primary feature, including a subset of congenital conditions (ie, chromosomal anomalies and congenital birth defects), neonatal conditions (ie, jaundice, preterm birth, and sepsis), infectious diseases (ie, COVID-19, cystic echinococcosis, malaria, syphilis, and Zika virus disease), and diabetic neuropathy. By conducting a sequela-level analysis of the health outcomes for these conditions, only cases where nervous system damage occurred were included, and YLDs were recalculated to isolate the non-fatal burden directly attributable to nervous system health loss. A comorbidity correction was used to calculate total prevalence of all conditions that affect the nervous system combined.FindingsGlobally, the 37 conditions affecting the nervous system were collectively ranked as the leading group cause of DALYs in 2021 (443 million, 95% UI 378–521), affecting 3·40 billion (3·20–3·62) individuals (43·1%, 40·5–45·9 of the global population); global DALY counts attributed to these conditions increased by 18·2% (8·7–26·7) between 1990 and 2021. Age-standardised rates of deaths per 100 000 people attributed to these conditions decreased from 1990 to 2021 by 33·6% (27·6–38·8), and age-standardised rates of DALYs attributed to these conditions decreased by 27·0% (21·5–32·4). Age-standardised prevalence was almost stable, with a change of 1·5% (0·7–2·4). The ten conditions with the highest age-standardised DALYs in 2021 were stroke, neonatal encephalopathy, migraine, Alzheimer's disease and other dementias, diabetic neuropathy, meningitis, epilepsy, neurological complications due to preterm birth, autism spectrum disorder, and nervous system cancer.InterpretationAs the leading cause of overall disease burden in the world, with increasing global DALY counts, effective prevention, treatment, and rehabilitation strategies for disorders affecting the nervous system are needed

Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations. METHODS The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model-a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates-with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality-which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds. FINDINGS The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2-100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1-290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1-211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4-48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3-37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7-9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles. INTERPRETATION Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere. FUNDING Bill & Melinda Gates Foundation

Development of a modern catalytic system for the production of C3+ aliphatic alcohols by the Fischer-Tropsch method

This thesis deals with converting a mixture of H2 and CO, also referred to as syngas or producer gas, to higher or mixed alcohols and other fuels through a process called Fischer Tropsch Synthesis (FTS). It is a beneficial pathway that minimizes the dependence on oil and similar fossil fuels which contribute to rapid climate change by releasing harmful greenhouse gases. The syngas used in FTS, is generally obtained through gasification of biomass to make the entire process renewable and to make the resulting fuel carbon neutral. The products are pure due to prior cleaning of syngas mixture to remove oxides of nitrogen, sulphur and other particulate matter, before the process, thereby drastically reducing the net exhaust gas emissions. The major objective of this project is to design a novel catalyst system and subject it to a series of experimentation for testing its selectivity towards alcohols. This is because the present catalytic systems are either very expensive to assemble or confer to a low yield. Two cobalt (Co) based catalysts, one without a promoter and the other which is promoted by zirconium (Zr), are prepared. The activity and selectivity of Co catalysts are finally compared with the existing Swedish Biofuels AB’s Iron (Fe) based catalyst promoted by copper (Cu) and chromium (Cr) along with characterization of the optimum reaction parameters like temperature, pressure, GHSV and syngas ratio for FTS. Aqueous incipient impregnation approach was adopted wherein the Co active metal and Zr promoter (only in second catalyst) are introduced step-wise on a ϒ-alumina support to synthesize the catalyst after which it is heat treated through drying, calcination and reduction to obtain the active Co metal catalyst. A high temperature FTS, was employed for the yield of alcohols and other gasoline derivatives according to literature. Finally, the liquid and gaseous products are analyzed through GC or GC/MS analysis techniques. The unpromoted Co catalyst’s activity is regarded as a failure due to satisfactory results. There were a few problems associated with the catalyst alone like poor mechanical stability that could be attributed to the use of an incorrect binder. Other problems included methanation due to haphazard temperature variations and inefficient catalyst reduction. For the promoted Co catalyst, the yield of alcohols and hydrocarbons was significantly higher than the unpromoted Co catalyst. A temperature of 300 °C, a GHSV of 360 h-1 , a pressure of 10 bar and a H2:CO ratio of 1.3:1 were the optimal background conditions for FTS. Higher temperature caused methanation and reduced the chain growth probability factor, α, that resulted in the formation of lower hydrocarbons only. Any increase in gas ratio and GHSV, also increased the rate of methane formation and caused diffusion limitations. For a one-stage setup with the reversal of exhaust gases, the conversion rates of CO and H2 were quite promising. This success can be attributed to a higher calcination temperature that increased the degree of reduction of Co due to formation of promoter oxides thereby enabling CO hydrogenation and H2 insertion. It helped to reduce CO2 formation as well. Even for the Fe catalyst, a low temperature, a low GHSV and low syngas ratio were preferred. But unlike its Co counterpart, a higher pressure favored an increase in yield of alcohols and other long chain hydrocarbons. Fe’s ability to support WGS reaction disturbed the molar ratio of CO and also released more CO2 that could affect the rate of syngas conversion. But, on the whole, Fe catalyst was efficient than Co catalyst for alcohol synthesis. The overall yield of alcohols was just 5% of the liquid products. Nearly 86% of the alcohol fraction comprised of C1, C2 and C3 alcohols alone and very few C4, C5 and C6 alcohols were obtained.Denna avhandling behandlar omvandling av en blandning av H2 och CO, även kallad syngas eller producentgas, till högre eller blandade alkoholer och andra bränslen genom en process som kallas Fischer Tropsch Synthesis (FTS). Det är en bra väg som minimerar beroendet av olja och liknande fossila bränslen som bidrar till snabba klimatförändringar genom att släppa ut skadliga växthusgaser. Syngasen som används i FTS erhålls generellt genom förgasning av biomassa för att göra hela processen förnybar och för att göra det resulterande bränslet kolneutralt. Produkterna är rena på grund av föregående rengöring av syngasblandningen för att avlägsna kväveoxider, svavel och annat partikelformigt material före processen och därigenom drastiskt minska utsläppen av avgaserna. Huvudsyftet med detta projekt är att utforma ett nytt katalysatorsystem och utsätta det för en serie experiment för att testa dess selektivitet gentemot alkoholer. Detta beror på att de nuvarande katalytiska systemen antingen är mycket dyra att montera eller ge ett lågt utbyte. Två koboltbaserade (Co) -baserade katalysatorer, en utan en promotor och den andra som befordras av zirkonium (Zr), framställs. Aktiviteten och selektiviteten hos Co-katalysatorer jämförs slutligen med de befintliga Swedish Biofuels AB: s Iron (Fe) -baserade katalysator som främjas av koppar (Cu) och krom (Cr) tillsammans med karaktärisering av de optimala reaktionsparametrarna som temperatur, tryck, GHSV och syngasförhållande för FTS. Vattenhaltig begynnande impregneringsmetod användes där den Co-aktiva metallen och Zr-promotorn (endast i den andra katalysatorn) införs stegvis på ett ϒ-aluminiumoxidstöd för att syntetisera katalysatorn, varefter den värmebehandlas genom torkning, kalcering och reduktion för att erhålla aktiv Co-metallkatalysator. En hög temperatur FTS användes för utbytet av alkoholer och andra bensinderivat enligt litteratur. Slutligen analyseras de flytande och gasformiga produkterna genom GC- eller GC / MS-analystekniker. Den outpromoterade Co-katalysatorns aktivitet betraktas som ett misslyckande på grund av tillfredsställande resultat. Det fanns några problem associerade med katalysatorn ensam som dålig mekanisk stabilitet som kunde tillskrivas användningen av ett felaktigt bindemedel. Andra problem inkluderade metanering på grund av variationer i slumpmässiga temperaturer och ineffektiv katalysatorreduktion. För den befordrade Co-katalysatorn var utbytet av alkoholer och kolväten betydligt högre än den opromoterade Co-katalysatorn. En optimal temperatur på 300 ° C, en GHSV på 360 h-1, ett tryck av 10 bar och ett H2: CO-förhållande på 1,3: 1 var de optimala bakgrundsbetingelserna för FTS. Högre temperatur orsakade metanering och reducerade sannolikhetsfaktorn för kedjan tillväxt, a, vilket resulterade i bildandet av endast lägre kolväten. Varje ökning av gasförhållandet och GHSV, ökade också metanbildningshastigheten och orsakade diffusionsbegränsningar. För en inställning i ett steg med reversering av avgaser var omvandlingsgraden för CO och H2 ganska lovande. Denna framgång kan tillskrivas en högre kalcineringstemperatur som ökade graden av reduktion av Co på grund av bildning av promotoroxider och därigenom möjliggör CO-hydrering och H2-införing. Det hjälpte också till att minska koldioxidbildningen. Även för Fe-katalysatorn föredrog man en låg temperatur, ett lågt GHSV och lågt syngasförhållande. Men till skillnad från Co-motsvarigheten gynnade ett högre tryck en ökning av utbytet av alkoholer och andra långkedjiga kolväten. Fe: s förmåga att stödja WGS-reaktion störde det molära förhållandet CO och frigav också mer CO2 som kan påverka hastigheten på syngasomvandlingen. Men i stort sett var Fe-katalysator mer effektiv än Cokatalysator för alkoholsyntes. Det totala utbytet av alkoholer var bara 5% av de flytande produkterna. Nästan 86% av alkoholfraktionen bestod av C1-, C2- och C3-alkoholer enbart och mycket få C4-, C5- och C6-alkoholer erhölls

Development of a modern catalytic system for the production of C3+ aliphatic alcohols by the Fischer-Tropsch method

This thesis deals with converting a mixture of H2 and CO, also referred to as syngas or producer gas, to higher or mixed alcohols and other fuels through a process called Fischer Tropsch Synthesis (FTS). It is a beneficial pathway that minimizes the dependence on oil and similar fossil fuels which contribute to rapid climate change by releasing harmful greenhouse gases. The syngas used in FTS, is generally obtained through gasification of biomass to make the entire process renewable and to make the resulting fuel carbon neutral. The products are pure due to prior cleaning of syngas mixture to remove oxides of nitrogen, sulphur and other particulate matter, before the process, thereby drastically reducing the net exhaust gas emissions. The major objective of this project is to design a novel catalyst system and subject it to a series of experimentation for testing its selectivity towards alcohols. This is because the present catalytic systems are either very expensive to assemble or confer to a low yield. Two cobalt (Co) based catalysts, one without a promoter and the other which is promoted by zirconium (Zr), are prepared. The activity and selectivity of Co catalysts are finally compared with the existing Swedish Biofuels AB’s Iron (Fe) based catalyst promoted by copper (Cu) and chromium (Cr) along with characterization of the optimum reaction parameters like temperature, pressure, GHSV and syngas ratio for FTS. Aqueous incipient impregnation approach was adopted wherein the Co active metal and Zr promoter (only in second catalyst) are introduced step-wise on a ϒ-alumina support to synthesize the catalyst after which it is heat treated through drying, calcination and reduction to obtain the active Co metal catalyst. A high temperature FTS, was employed for the yield of alcohols and other gasoline derivatives according to literature. Finally, the liquid and gaseous products are analyzed through GC or GC/MS analysis techniques. The unpromoted Co catalyst’s activity is regarded as a failure due to satisfactory results. There were a few problems associated with the catalyst alone like poor mechanical stability that could be attributed to the use of an incorrect binder. Other problems included methanation due to haphazard temperature variations and inefficient catalyst reduction. For the promoted Co catalyst, the yield of alcohols and hydrocarbons was significantly higher than the unpromoted Co catalyst. A temperature of 300 °C, a GHSV of 360 h-1 , a pressure of 10 bar and a H2:CO ratio of 1.3:1 were the optimal background conditions for FTS. Higher temperature caused methanation and reduced the chain growth probability factor, α, that resulted in the formation of lower hydrocarbons only. Any increase in gas ratio and GHSV, also increased the rate of methane formation and caused diffusion limitations. For a one-stage setup with the reversal of exhaust gases, the conversion rates of CO and H2 were quite promising. This success can be attributed to a higher calcination temperature that increased the degree of reduction of Co due to formation of promoter oxides thereby enabling CO hydrogenation and H2 insertion. It helped to reduce CO2 formation as well. Even for the Fe catalyst, a low temperature, a low GHSV and low syngas ratio were preferred. But unlike its Co counterpart, a higher pressure favored an increase in yield of alcohols and other long chain hydrocarbons. Fe’s ability to support WGS reaction disturbed the molar ratio of CO and also released more CO2 that could affect the rate of syngas conversion. But, on the whole, Fe catalyst was efficient than Co catalyst for alcohol synthesis. The overall yield of alcohols was just 5% of the liquid products. Nearly 86% of the alcohol fraction comprised of C1, C2 and C3 alcohols alone and very few C4, C5 and C6 alcohols were obtained.Denna avhandling behandlar omvandling av en blandning av H2 och CO, även kallad syngas eller producentgas, till högre eller blandade alkoholer och andra bränslen genom en process som kallas Fischer Tropsch Synthesis (FTS). Det är en bra väg som minimerar beroendet av olja och liknande fossila bränslen som bidrar till snabba klimatförändringar genom att släppa ut skadliga växthusgaser. Syngasen som används i FTS erhålls generellt genom förgasning av biomassa för att göra hela processen förnybar och för att göra det resulterande bränslet kolneutralt. Produkterna är rena på grund av föregående rengöring av syngasblandningen för att avlägsna kväveoxider, svavel och annat partikelformigt material före processen och därigenom drastiskt minska utsläppen av avgaserna. Huvudsyftet med detta projekt är att utforma ett nytt katalysatorsystem och utsätta det för en serie experiment för att testa dess selektivitet gentemot alkoholer. Detta beror på att de nuvarande katalytiska systemen antingen är mycket dyra att montera eller ge ett lågt utbyte. Två koboltbaserade (Co) -baserade katalysatorer, en utan en promotor och den andra som befordras av zirkonium (Zr), framställs. Aktiviteten och selektiviteten hos Co-katalysatorer jämförs slutligen med de befintliga Swedish Biofuels AB: s Iron (Fe) -baserade katalysator som främjas av koppar (Cu) och krom (Cr) tillsammans med karaktärisering av de optimala reaktionsparametrarna som temperatur, tryck, GHSV och syngasförhållande för FTS. Vattenhaltig begynnande impregneringsmetod användes där den Co-aktiva metallen och Zr-promotorn (endast i den andra katalysatorn) införs stegvis på ett ϒ-aluminiumoxidstöd för att syntetisera katalysatorn, varefter den värmebehandlas genom torkning, kalcering och reduktion för att erhålla aktiv Co-metallkatalysator. En hög temperatur FTS användes för utbytet av alkoholer och andra bensinderivat enligt litteratur. Slutligen analyseras de flytande och gasformiga produkterna genom GC- eller GC / MS-analystekniker. Den outpromoterade Co-katalysatorns aktivitet betraktas som ett misslyckande på grund av tillfredsställande resultat. Det fanns några problem associerade med katalysatorn ensam som dålig mekanisk stabilitet som kunde tillskrivas användningen av ett felaktigt bindemedel. Andra problem inkluderade metanering på grund av variationer i slumpmässiga temperaturer och ineffektiv katalysatorreduktion. För den befordrade Co-katalysatorn var utbytet av alkoholer och kolväten betydligt högre än den opromoterade Co-katalysatorn. En optimal temperatur på 300 ° C, en GHSV på 360 h-1, ett tryck av 10 bar och ett H2: CO-förhållande på 1,3: 1 var de optimala bakgrundsbetingelserna för FTS. Högre temperatur orsakade metanering och reducerade sannolikhetsfaktorn för kedjan tillväxt, a, vilket resulterade i bildandet av endast lägre kolväten. Varje ökning av gasförhållandet och GHSV, ökade också metanbildningshastigheten och orsakade diffusionsbegränsningar. För en inställning i ett steg med reversering av avgaser var omvandlingsgraden för CO och H2 ganska lovande. Denna framgång kan tillskrivas en högre kalcineringstemperatur som ökade graden av reduktion av Co på grund av bildning av promotoroxider och därigenom möjliggör CO-hydrering och H2-införing. Det hjälpte också till att minska koldioxidbildningen. Även för Fe-katalysatorn föredrog man en låg temperatur, ett lågt GHSV och lågt syngasförhållande. Men till skillnad från Co-motsvarigheten gynnade ett högre tryck en ökning av utbytet av alkoholer och andra långkedjiga kolväten. Fe: s förmåga att stödja WGS-reaktion störde det molära förhållandet CO och frigav också mer CO2 som kan påverka hastigheten på syngasomvandlingen. Men i stort sett var Fe-katalysator mer effektiv än Cokatalysator för alkoholsyntes. Det totala utbytet av alkoholer var bara 5% av de flytande produkterna. Nästan 86% av alkoholfraktionen bestod av C1-, C2- och C3-alkoholer enbart och mycket få C4-, C5- och C6-alkoholer erhölls

Numerical investigation of dimple-texturing on the turning performance of hardened AISI H-13 steel

Forming micro-dimples nearer to the cutting edge on the rack face of the tungsten carbide cutting inserts will positively influence the machinability. However, it is challenging to machine the perfect micro-dimple dimensions by utilizing the available machining techniques. Finite element analysis can be an efficient way to observe the influence of dimple-texture area density, micro-dimple size, and various micro-dimple shapes on cutting inserts' machinability. This paper numerically analyses the impact of micro-dimple-textured cutting inserts in dry machining of AISI H-13 steel using AdvantEdge (virtual machining and finite element analysis software). Micro-dimples are formed on the rack face of tungsten carbide cutting inserts to observe the effect of dimple-textured cutting inserts on machinability compared to non-textured cutting inserts in terms of micro-dimple shape, micro-dimple size, and micro-dimple area density ratio. Their outcomes are analysed in terms of chip-insert contact length, main cutting force, and thrust force. It is observed that micro-dimple textured cutting inserts exhibit minimal main cutting force and thrust force in line with increasing the cutting insert life span. The abrasive wear was reduced in dimple-textured cutting inserts due to minimal contact between the cutting insert and chip developed compared to non-textured cutting inserts

Double D-pi-A Dye Linked by 2,2'-Bipyridine Dicarboxylic Acid: Influence of para- and meta-Substituted Carboxyl Anchoring Group

Starting from 2,2-bipyridine dicarboxylic acid, two new (D--A)(2) sensitizers, including m-DA with the carboxyl anchoring group substituted meta to the donor-bridge moiety and p-DA with a para-substituted anchoring group, were synthesized in order to evaluate the impact of the position of the anchoring group on the optical, electrochemical, and photovoltaic properties of dye-sensitized solar cells. p-DA exhibits red-shifted absorption behavior compared to m-DA, owing to the more efficiently extended -conjugation with para substitution. Both m-DA and p-DA are adsorbed on the mesoporous TiO2 surface by using both of their carboxylic acid groups in a bianchoring mode, which is confirmed through attenuated total reflectance FTIR analysis. Red-shifted absorption of p-DA assists the achievement of a red-shifted incident photon-to-electron conversion efficiency and a higher short-circuit current density than m-DA. The photogenerated electron lifetime in TiO2 is also found to be higher for para substituted p-DA than the meta-substituted m-DA, which results in a higher open-circuit voltage. All of the results suggest that dicarboxyl-2,2-bipyridine can be used as an acceptor for metal-free organic sensitizers. However, the anchoring segments should be adjusted to the favorable position of the corresponding donor-bridge moieties for better conjugation