Compressive Strength of Concrete using Fly Ash and Rice Husk Ash: A Review

Decreasing our over-reliance on cement as an ingredient in the making of concrete due to its contribution to the CO2 emissions has led to numerous researches been conducted to find suitable replacement for cement in concrete mixes.  Materials like fly ash, ground granulated blast furnace slag, silica fume, rice husk ash and metakaolin among others have been identified as materials that can at the very least be used as a replacement for cement in concrete mix. These materials are referred to as supplementary cementitious materials (SCMs). This paper reviewed the work that has been done on the use of fly ash and rice husk ash as partial replacements for concrete, its chemical composition and its effect on the compressive strength of concrete. Charts, tables and figures were employed as tools to study the various chemical compounds of fly ash and rice husk ash. It was seen that depending on how the coal or rice husk was initially processed the percentage of some of the minor compounds like Sodium oxide (Na2O), Titanium oxide (TiO2) and Phosphorus pentoxide (P2O5) were sometimes very low or not recorded as part of the final product.  The data on the compressive strength of concrete after fly ash and rice husk ash had been added in percentage increments of 0%, 10%, 20%, 30%, 40%, 50% and 0%, 5%, 7.5%, 10%, 12.5%, 15% respectively analysed over a minimum period of 7 days and a maximum period of 28 days found out that the optimal percentage partial replacement of fly ash and rice husk ash for a strong compressive concrete strength is 30% of fly ash and 7.5% of rice husk ash

Africa GreenCo and the Independent Off-Taker Model: Beyond ‘Single-Buyer’ Power Markets and Uncreditworthy Utilities

Africa GreenCo is challenging the existing model of how new private-sector-funded grid-scale power is brought online. By introducing the first non-government-owned buyer of renewable energy in sub-Saharan Africa—a region with few creditworthy public utilities—GreenCo will act as a bankable counterparty for independent power producers. The company aims to catalyse private investment and boost the growth of additional clean generation capacity in support of climate change mitigation, adaptation, and energy access. The paper reviews modelled investment- and climate resilience impacts

Matrices with restricted entries and q-analogues of permutations

We study the functions that count matrices of given rank over a finite field with specified positions equal to zero. We show that these matrices are $q$-analogues of permutations with certain restricted values. We obtain a simple closed formula for the number of invertible matrices with zero diagonal, a $q$-analogue of derangements, and a curious relationship between invertible skew-symmetric matrices and invertible symmetric matrices with zero diagonal. In addition, we provide recursions to enumerate matrices and symmetric matrices with zero diagonal by rank, and we frame some of our results in the context of Lie theory. Finally, we provide a brief exposition of polynomiality results for enumeration questions related to those mentioned, and give several open questions.Comment: 29 pages, 2 figures, v2: one additional result, some formulas simplified, and a new reference; v3: corrected typo

Evaluation of predictors for choledocholithiasis and assessment of outcomes after treatment: A historical cohort study

BACKGROUND: Common bile duct (CBD) stones are seen in 5% to 10% of those undergoing cholecystectomy. Missed CBD stones pose a risk of recurrent symptoms of abdominal pain, pancreatitis, and cholangitis unless identified at presentation. Therefore identifying the key predictors at presentation is of great value. OBJECTIVES: 1. To study the clinical, laboratory and radiological findings of patients diagnosed with common bile duct stones. 2. To study the current practice of managing this condition in our tertiary care hospital (Christian Medical College and Hospital). 3. To obtain data of a one year follow up of these patients who had undergone treatment for choledocholithiasis. METHODS: Cohort of patients diagnosed with choledocholithiasis who presented to the outpatient clinic of Hepatic Pancreatic and Biliary Surgery, General Surgery and Gastroenterology departments at Christian Medical College, Vellore from July 2008 to June 2012 were included in the study, and one year follow up data was also collected. The presenting history, clinical examination, laboratory tests and radiological imaging in the patients were recorded in the performa. RESULTS: The management practice in this tertiary care centre along with the various relevant clinical, biochemical and imaging parameters were identified. Abdominal pain was the common complaint (76%). Jaundice was a significant predictor for failure of ERCP. Abdominal ultrasonography commonly showed CBD dilation (85.4%) and intrahepatic biliary radical dilatation. MRI was the most sensitive to demonstrate CBD stone (86.6%). ERCP was the primary modality of treatment. CBD exploration was the treatment of choice in case of failed ERCP and stone extraction. There were recurrent CBD stones in 5% of the follow-up population. DISCUSSION: The most common clinical presentation of choledocholithiasis was abdominal pain. The presence of a dilated common bile duct of above 10mm associated with intrahepatic biliary dilatation was the commonest initial radiological finding. Abdominal ultrasound was an effective modality to pick up common bile duct stones but MRI had the best sensitivity. ERCP appeared to be the effective and preferred primary intervention of choice with failure rates being more in those having jaundice and dilated bile ducts. Delay in laparoscopic cholecystectomy following ERCP lead to a higher conversion rate to an open procedure. Serum alkaline phosphatase appeared to the best marker on follow up

Viability and Reproducibility of Additively Manufactured Shape Memory Alloys and High Temperature Shape Memory Alloys

Shape memory alloys (SMAs) are metals that can “remember” the shape they were in before deformation and can return to that shape upon heating. These alloys have a structure that changes based on applied stress and temperature and are promising candidates for solid-state actuators in the robotics and aerospace industries. Conventionally manufactured SMAs must undergo further processing to be formed into desired structures. With further processing there is a greater chance of introducing inclusions such as oxygen and carbon, which greatly affect the transformation temperatures of SMAs, as well as forming cracks and other structural defects. Additive manufacturing (AM) of SMAs combines alloy production and forming into a single step, reducing extraneous processing steps. AM SMAs do not currently perform as well mechanically as their conventionally manufactured counterparts. Tensile shape memory actuation was characterized for nickel-titanium (NiTi) SMAs fabricated using the laser powder bed fusion (L-PBF) AM process and two different sets of processing parameters in order to determine the viability of AM SMAs. While reversible tensile shape memory behavior was observed in both cases, the specimens fabricated with a shorter hatch spacing exhibited higher transformation temperatures, lower actuation strain, and lower irrecoverable strain compared to the specimens fabricated with wider hatch spacing. The actuation strain of the L-PBF samples was lower than that of conventionally manufactured NiTi SMA specimens. High temperature shape memory alloys (HTSMAs) are a class of SMAs that have elements added to increase their transformation temperatures for use in high-temperature environments to prevent accidental actuation. The nickel-titanium-hafnium (NiTiHf) system has shown significant promise as an HTSMA with higher strength and work output than NiTi. Batches of NiTiHf produced in previous studies have shown variation in fatigue life and transformation temperatures despite similar compositions. A parameter called “actuation potential” was created to quantify hypothetical performance of each batch in actuator applications. Carbide content, precipitate size, stress-strain curves, stress-temperature phase diagrams, and transformation strain data from four batches of NiTiHf were used to search for the underlying causes of batch-to-batch variation in NiTiHf. Correlations of carbide content and precipitate size with actuation potential were observed, and hypotheses as to why these variations affect performance are proposed

The transmissibility of novel Coronavirus in the early stages of the 2019-20 outbreak in Wuhan: Exploring initial point-source exposure sizes and durations using scenario analysis.

Background: The current novel coronavirus outbreak appears to have originated from a point-source exposure event at Huanan seafood wholesale market in Wuhan, China. There is still uncertainty around the scale and duration of this exposure event. This has implications for the estimated transmissibility of the coronavirus and as such, these potential scenarios should be explored.   Methods: We used a stochastic branching process model, parameterised with available data where possible and otherwise informed by the 2002-2003 Severe Acute Respiratory Syndrome (SARS) outbreak, to simulate the Wuhan outbreak. We evaluated scenarios for the following parameters: the size, and duration of the initial transmission event, the serial interval, and the reproduction number (R0). We restricted model simulations based on the number of observed cases on the 25th of January, accepting samples that were within a 5% interval on either side of this estimate. Results: Using a pre-intervention SARS-like serial interval suggested a larger initial transmission event and a higher R0 estimate. Using a SARs-like serial interval we found that the most likely scenario produced an R0 estimate between 2-2.7 (90% credible interval (CrI)). A pre-intervention SARS-like serial interval resulted in an R0 estimate between 2-3 (90% CrI). There were other plausible scenarios with smaller events sizes and longer duration that had comparable R0 estimates. There were very few simulations that were able to reproduce the observed data when R0 was less than 1. Conclusions: Our results indicate that an R0 of less than 1 was highly unlikely unless the size of the initial exposure event was much greater than currently reported. We found that R0 estimates were comparable across scenarios with decreasing event size and increasing duration. Scenarios with a pre-intervention SARS-like serial interval resulted in a higher R0 and were equally plausible to scenarios with SARs-like serial intervals

The phenomenology of voice-hearing and two concepts of voice

The experiences described in the VIP transcripts are incredibly varied and yet frequently explicitly labelled by participants as "voices." How can we make sense of this? If we reflect carefully on uses of the word "voice", we see that it can express at least two entirely different concepts, which pick out categorically different phenomena. One concept picks out a speech sound (e.g. "This synthesizer has a "voice" setting"). Another concept picks out a specific agent (e.g. "I hear two voices: one is a ten year-old boy…"). This chapter explores how these two concepts are related to one another in the context of voice-hearing

Narrow Radiative Recombination Continua: A Signature of Ions Crossing the Contact Discontinuity of Astrophysical Shocks

X-rays from planetary nebulae (PNs) are believed to originate from a shock driven into the fast stellar wind (v ~ 1000 km/s) as it collides with an earlier circumstellar slow wind (v ~ 10 km/s). In theory, the shocked fast wind (hot bubble) and the ambient cold nebula can remain separated by magnetic fields along a surface referred to as the contact discontinuity (CD) that inhibits diffusion and heat conduction. The CD region is extremely difficult to probe directly owing to its small size and faint emission. This has largely left the study of CDs, stellar-shocks, and the associated micro-physics in the realm of theory. This paper presents spectroscopic evidence for ions from the hot bubble (kT ~ 100 eV) crossing the CD and penetrating the cold nebular gas (kT ~ 1 eV). Specifically, a narrow radiative recombination continuum (RRC) emission feature is identified in the high resolution X-ray spectrum of the PN BD+30 3639 indicating bare C VII ions are recombining with cool electrons at kT_e=1.7+-1.3 eV. An upper limit to the flux of the narrow RRC of H-like C VI is obtained as well. The RRCs are interpreted as due to C ions from the hot bubble of BD+30 3639 crossing the CD into the cold nebula, where they ultimately recombine with its cool electrons. The RRC flux ratio of C VII to C VI constrains the temperature jump across the CD to Delta kT > 80 eV, providing for the first time direct evidence for the stark temperature disparity between the two sides of an astrophysical CD, and constraining the role of magnetic fields and heat conduction accordingly. Two colliding-wind binaries are noted to have similar RRCs suggesting a temperature jump and CD crossing by ions may be a common feature of stellar wind shocks.Comment: 14 pages, 5 figures, accepted to ApJ. Corrected typos, minor modifications to eq. 5 and corresponding tex

Citizenship and Socio-Political Integration: A Person-Oriented Analysis Among Russian-Speaking Minorities in Estonia, Finland and Norway

This survey study utilized a person-oriented approach to explore the patterns of socio-political integration among Russian-speaking minority group members in three neighboring countries in the Baltic area: Estonia (n = 482), Finland (n = 252), and Norway (n = 215). Three profiles were obtained in all countries: critical integration, separation, and assimilation. In the whole sample, critical integration was the most common acculturation profile. After the profiles were established, they were examined vis-a-vis citizenship and integration context to see, whether and to what extent, the objective (i.e., citizenship) and subjective (i.e., perceived social status and sense of belonging) socio-political integration of Russian-speakers corresponded with each other. Critical integration and separation were the most common profiles among participants holding national citizenship of the country of residence, while foreign citizenship was not related to any specific profile. Separation was rare among participants holding dual citizenship, but it was the most common profile among participants with undetermined citizenship. Also, intergroup context was associated with socio-political integration: critical integration and separation were the most common profiles of Russian-speakers in Estonia, critical integration and assimilation profiles in Finland, and assimilation profile in Norway. The results are discussed in relation to previous variable-oriented research and official integration policies of the countries studied.Peer reviewe