Добірка наукової літератури з теми "NPISH"

The limited availability of cadaveric human donor pancreata as well as the incomplete success of the Edmonton protocol for human islet allografts fasten search for new sources of insulin the producing cells for substitution cell therapy of insulin-dependent diabetes mellitus (T1DM). Starting from isolated neonatal porcine pancreatic islets (NPIs), we have obtained cell monolayers that were exposed to microencapsulated monolayered Sertoli cells (ESCs) for different time periods (7, 14, 21 days). To assess the development of the cocultured cell monolayers, we have studied either endocrine cell phenotype differentiation markers or c-kit, a hematopoietic stem cell marker, has recently been involved with growth and differentiation ofβ-cell subpopulations in human as well as rodent animal models. ESC which were found to either accelerate maturation and differentiation of the NPIsβ-cell phenotype or identify an islet cell subpopulation that was marked positively for c-kit. The insulin/c-kit positive cells might represent a new, still unknown functionally immatureβ-cell like element in the porcine pancreas. Acceleration of maturation and differentiation of our NPI cell monolayers might generate a potential new opportunity to develop insulin-producing cells that may suite experimental trials for cell therapy of T1DM.

Thesis (S.M. in Engineering and Management)--Massachusetts Institute of Technology, Engineering Systems Division, System Design and Management Program, February 2011.
"November 2010." Cataloged from PDF version of thesis.
Includes bibliographical references (p. 57-58).
This thesis focuses on the use of non-pharmaceutical interventions (NPIs) during the time of the 2009 HINI pandemic and its possible relation to RO and R(t). RO is defined as the mean number of people that a newly infected person will subsequently infect in a completely susceptible population whereas R(t) is the average number of new infections by an infectious individual at time t. RO is important for understanding the severity of an influenza outbreak while R(t) is a necessary tool to measure the progression of infection rate over time. A high RO value (more than 2) generally corresponds to a more serious outbreak. This thesis discusses a town in Mexico named La Gloria, which is thought to be the place where the HINI pandemic started, and the subsequent implementation of NPIs in Mexico City as the virus spread and people became aware of its novelty. An evaluation of Mexico's response to HlNl suggests that the emphasis on the use of NPIs may have related to a decreasing RO value. Further investigation of this relationship using news articles and Google Insights also shows interesting potential correlations. In short my thesis focuses on the possible relationship between ROs and NPIs in a pandemic setting.
by Sahar Hashmi.
S.M.in Engineering and Management

Mestrado em Engenharia Química
A EGEO Solventes S.A. atua na área da gestão de resíduos, sendo a sua especialidade a regeneração de solventes, com vista à sua valorização. O processo de regeneração de solventes foca-se na destilação descontínua. Nas instalações, as colunas de destilação são auxiliadas por condensadores, por forma a recuperar o solvente regenerado. Esta condensação é efetuada com recurso a água de refrigeração. Após a passagem nos condensadores, esta é então alimentada a torres refrigeração, voltando a arrefecer para ser recirculada aos condensadores. No decorrer do processo de recuperação de solventes foram identificados problemas relacionados com a rede de permutadores de calor. Em determinadas condições de operação, denotou-se uma fraca condensação, fraco arrefecimento da água nas torres de arrefecimento e uma constante cavitação nas bombas do circuito de água de arrefecimento. Recorrendo a uma análise aos balanços de massa e energia do sistema, bem como a um balanço à quantidade de movimento, foi possível diagnosticar o baixo rendimento dos permutadores e das torres de arrefecimento. Por forma a ser possível calcular as perdas de carga, foi efetuado um levantamento de todas as tubagens e criado um diagrama isométrico para melhor leitura da estrutura real. Foi feita uma análise aos circuitos de água e às bombas, sendo possível determinar como causa de esforço das bombas um mau dimensionamento das tubagens. Adicionalmente, foram ainda estudados os caminhos preferenciais da água no circuito. No que diz respeito ao fraco arrefecimento nas torres de refrigeração foi também estudada a alimentação das torres, pelo que a causa encontrada consistia na baixa pressão da água à entrada das torres. Com recurso ao simulador de processos comercial Aspen Plus® foi estudada a influência da água de arrefecimento no processo, e efetuada uma otimização do circuito. Foi efetuada uma análise económica mostrando ser possível redução em 76% dos gastos e custos associados ao processo. Por fim, foram propostas modificações ao processo, baseadas nos resultados obtidos na otimização com principal incidência na redução das perdas de carga e melhor utilização da água de arrefecimento.
EGEO Solventes S.A. is a waste management company, focused in solvent regeneration. The solvent regeneration process focus on distillation. At the facilities, the distillation columns are assisted by condensers in order to condense the solvent. This condensation is performed using water cooling. After passing the condenser, the water is then fed to cooling towers to cool back to, once again, return to the circuit. During the solvent recovery process, there have been identified problems related to the heat exchanger network. Under certain operating conditions, it was denoted a weak performance both condensators and cooling towers and constant cavitation in the pumps of the water cooling circuit. Using an analysis of mass, energy and momentum balances, it was possible to diagnose the problems identified: poor condensation in the condensers and weak cooling in the cooling towers. Analysis of the water circuit and the pumps were made and it was possible to determine that the cavitation in pumps was caused by the head loss in the pipe network. Additionally, it was also studied the preferred paths of water in the circuit. Concerning the weak cooling in the cooling towers, was found that the cause for the weak efficiency was the water feed’s low pressure. Using the commercial process’ simulator Aspen Plus®, the influence of the cooling water in the process had been studied and a circuit optimization was. An economic analysis was performed, showing it is possible to reduce process’ costs by 76%. Finally, changes to the process were proposed, based on the obtained optimization results.

Magister Scientiae - MSc (Physics)
Electron-mediated nuclear plasma interactions (NPIs), such as Nuclear Excitation by Electron Capture (NEEC) or Transition (NEET), can have a signi cant impact on nuclear cross sections in High Energy Density Plasmas (HEDPs). HEDP environments are found in nuclear weapons tests, National Ignition Facility (NIF) shots and in the cosmos where nucleosynthesis takes place. This thesis explores the impact of NPIs on highly excited nuclei. This impact is understood to be more intense in highly-excited nuclei states in the quasi-contiuum which is populated by nuclear reactions prior to their decay by spontaneous -ray emission.

Esta dissertação tem como objetivo estimar a Altura Livre Positiva de Aspiração (Net Pressure Suction Head, NPSH). Esta grandeza surgiu como uma resposta dos engenheiros ao elevado número de bombas que se danificavam devido a fenómenos de cavitação. Em 1932, o Hydraulic Institute propôs um método de deteção de cavitação através de um critério de redução de 3% da altura fornecida pela bomba. Atualmente, embora haja métodos mais evoluídos para identificar a presença de cavitação, o método dos 3% continua a ser utilizado pela indústria para caracterizar a pressão de aspiração de uma bomba. Esta dissertação tem como objetivo testar e validar a precisão deste método. Para tal foi utilizado o banco de ensaios presente no laboratório da Secção de Dinâmica dos Fluidos e Termodinâmica Aplicada da FCT-UNL. No início deste trabalho, este banco de ensaio não possuía a devida instrumentação para a determinação das curvas de NPSH, porém e no âmbito desta tese, modificou-se o mesmo de forma a que se pudesse determinar, não só a curva de NPSH(Q), mas como todas as curvas necessárias para caracterizar uma bomba centrífuga. Concluiu-se que apesar de haver métodos mais apurados para detetar cavitação com um banco de ensaios bem equipado, o método dos 3% de queda fornece resultados coerentes. Foram realizados ensaios onde obtiveram-se as curva H(Q), P(Q), e η(Q). As curvas NPSH(Q) foram conseguidas através de dois métodos diferentes. Concluiu- se que, embora muito semelhantes, não se sobrepunham devido à influência do erro dos sensores na leitura dos dados.

Since the beginning of the COVID-19 pandemic, countries worldwide have implemented a set of Non-Pharmaceutical Interventions (NPIs) as a way to face the evolution of the pandemic. In this dissertation we propose a detailed analysis of the evolution of the pandemic that considers the degree of restriction of NPIs from March 2020 to May 2021 and the reproduction rate in five countries: India, Brazil, United Kingdom, Israel and Portugal. In addition to this, we analyse the impact that Hofstede's cultural dimensions may have between implementations of various degrees of restriction of NPIs and the reproduction rate by applying machine learning models to understand whether cultural characteristics are useful information to improve reproduction rate predictions. To achieve these objectives, we follow the CRISP-DM methodology being that we gather data from Our World in Data COVID-19, Oxford COVID-19 Government Response Tracker and Hofstede Insights website. We show an in-depth and extensive analysis over these months of the pandemic which shows differences between the five countries that have implemented the same NPIs to different degrees and where culture plays an important role in each country's response to the various NPIs implemented.
Desde o início da pandemia COVID-19 que os países do mundo inteiro implementaram um conjunto de intervenções não farmacêuticas (NPIs) como forma de combater a evolução da pandemia. Nesta dissertação propomos uma análise detalhada da evolução da pandemia que considera o grau de restrição das NPIs desde Março de 2020 a Maio de 2021 e a taxa de reprodução em cinco países: India, Brasil, Reino Unido, Israel e Portugal. Além disto, analisamos o impacto que as dimensões culturais de Hofstede podem ter entre as implementações de vários graus de restrição de NPIs e a taxa de reprodução aplicando modelos de machine learning para compreender se as características culturais são informações úteis para melhorar as previsões da taxa de reprodução. Para concretizar estes objetivos, nós seguimos a metodologia do CRISP-DM sendo que, reunimos dados de Our World in Data COVID-19, Oxford COVID-19 Government Response Tracker e o website Hofstede Insights. Mostramos uma análise aprofundada e extensa ao longo destes meses da pandemia a qual mostra diferenças entre os cinco países que implementaram as mesmas NPIs em diferentes graus e em que a cultura desempenha um papel importante na resposta de cada país às várias NPIs implementadas.

Luminescent materials find numerous applications in recent times and have enriched human lives in several different ways. From display and lighting technologies to security, sensing and biological investigations, luminescent organic compounds have become indispensible and often preferred over their inorganic counterparts. The versatility of organic materials arises from their comparative low costs, ease of fine-tuning, low toxicity and the possibility to develop flexible devices. Even until very recent times, the investigations and usage of organic luminescent materials were mostly limited to solution-state properties. However, with progress of available characterisation techniques and parallel development of their usage in solid-state devices and other applications (e.g. security, forensics, sensing etc.), significantly greater attention has been paid to the development and investigations of solid-state emissive organic materials. In solid-state applications, apart from the molecular properties of any given material, their cumulative i.e. bulk physical properties are of even greater importance. Thus, investigations of structure-property relationships in organic luminescent compounds to understand their molecular and bulk properties are of fundamental interest. In this thesis, NPI (1,8-naphthalimide) and BODIPY (boron-dipyrromethene) dyes were investigated to provide a broad overview of their structure-property correlations. Among commonly encountered organic luminescent materials, NPIs and BODIPYs have emerged as two broad classes of luminescent organic compounds, finding applications as functional luminescent materials in various fields. However, lack of understanding for controlling the cumulative emissive properties of these compounds has limited their usage as active solid-state emitters in various applications. This thesis presents several new insights into the molecular and bulk emissive properties of these two classes of luminescent dyes (NPIs and BODIPYs). The contents of the six chapters contained in this thesis are summarised below. Chapter 1 summarises the available understanding of the basic concepts of photoluminescence and the design strategies to develop solid-state luminescent and AIE (aggregation-induced emission) active materials. This chapter also emphasises in the basic nature of the NPI and BODIPY compounds, their substitution patterns and their inherent characteristics and touches upon the relatively unexplored properties of NPI and BODIPY based materials. The importance and scope of the work reported in the thesis is outlined at the end of the chapter. Chapter 2 describes a detailed investigation of a series of seven (4-oxoaryl substituted) NPI compounds (1-7) providing an insight into the molecular and cumulative photophysical behaviour of these compounds. The low ICT characteristics of the NPIs, coupled with the twisted geometry, facilitated solid-state luminescence in these materials. The solution and solid-state luminescent properties of these compounds can be directly correlated to their structural rigidity, nature of substituents and solid-state intermolecular interactions (e.g. π-π stacking, C-H•••O interactions etc.). The solid-state crystal structures of the NPI siblings are profoundly affected by the pendant substituents. All of the NPIs (1-7) show antiparallel dimeric π-π stacking interactions in the solid-state which can further extend in parallel, alternate, orthogonal or lateral fashion depending on the steric and electronic nature of the C-4′ substituents. Structural investigations including Hirsfeld surface analysis methods reveal that while strongly interacting systems show weak to moderate emission in their condensed states, weakly interacting systems show strong emission yields under the same conditions. The nature of packing and extended structures also affects the emission colors of the NPIs in the solid-state. DFT computational studies were utilized to understand the molecular and cumulative electronic behavior of the NPIs. Apart from the investigation of solid-state luminescence, other functional potentials of these NPIs were also explored. One of the compounds (i.e. 4) shows chemodosimetric response towards aqueous Hg(II) species with a ‘turn-on’ response. Also, depending on the molecular flexibility of the compounds, promising AIEE (aggregation-induced emission enhancement) features were observed in these NPIs. Later (in Chapter 3), we developed a systematic investigation in a series of purely organic NPIs, restricting various parameters, to attain a thorough understanding of such AIEE properties. Chapter 3 describes a detailed experimental and computational study in order gain an insight into the AIE (aggregation-induced emission) and AIEE mechanisms in NPI compounds. Systematic structural perturbation was used to fine tune the luminescence properties of three new 1,8-naphthalimides (8-10) in solution and as aggregates. The NPIs (8-10) show blue emission in solution state and the fluorescence quantum yields depend on their molecular rigidity. In concentrated solutions of the NPIs, intermolecular interactions were found to result in quenching of fluorescence. In contrast, upon aggregation (in THF:H2O mixtures), two of the NPIs show aggregation-induced-emission-enhancement (AIEE). The NPIs also show moderately high solid-state emission quantum yields (~10-12.7 %). The AIEE behaviors of the NPIs depend on their molecular rigidity and nature of intermolecular interactions. The NPIs (8-10) show different extents of intermolecular (π-π and C-H•••O) interactions in their solid-state structures depending on their substituents. Detailed photophysical, computational and structural investigations suggest that only an optimal balance of structural flexibility and intermolecular communication is the effective recipe for achieving AIEE characteristics in these NPIs. Chapter 4 presents the design, synthesis and detailed investigations and potential applications of a series of NPI-BODIPY dyads (11-13). The NPI and BODIPY moieties in these dyads are electronically separated by oxoaryl bridges and the compounds only differ structurally with respect to methyl substitutions on the BODIPY fluorophore. The NPI and BODIPY moieties retain their optical features in these molecular dyads (11- 13). Dyads 11-13 show dual emission in solution state originating from the two separate fluorescent units. The variations of the dual emission in these compounds are controlled by the structural flexibility of the systems. The dyads also show significant AIES (Aggregation-Induced-Emission Switching) features upon formation of nano-aggregates in THF-H2O mixtures with visual changes in emission from green to red color. Whereas the flexible and aggregation prone system (i.e. compound 11) shows aggregation-induced enhancement of emission, rigid systems with less favorable intermolecular interactions (i.e. compound 12-13) show aggregation-induced quenching of emission. The emission-intensity vs. the structural-flexibility correlations were found to be reverse in solution and aggregated states. Photophysical and structural investigations suggest that the intermolecular interactions (e.g. π-π stacking etc.) play major role in controlling emission of these compounds in aggregated states. Similar trends were also observed in the solid-state luminescence of these compounds. The applications of the luminescent dyads 11-13 as live-cell imaging dyes was also investigated. Chapter 5 describes investigations of photophysical properties of a series of six BODIPY dyes (14-19) in which there is a systematic alteration of a common -C6H4Si(CH3)3 substituent. Inrelated constitutional isomers, the systematic increment of steric congestion and lowering of molecular symmetry around the BODIPY core result in a steady increment of solution and solid- state fluorescence quantum yields. The increasing fluorescence quantum yields (solution, solid state) with increasing steric congestions show that the molecular free rotation and aggregation-induced fluorescence quenching of BODIPYs can be successfully suppressed by lowering the flexibility of the molecules. Photophysical and DFT investigations reveal that the electronic band gap in any set of these constitutional isomers remain almost similar. However, the crystal structures of the compounds reveal that the solid-state colour and quantum yields of the compounds in solid-state are also related to the nature of intermolecular interactions. Chapter 6 demonstrates the use of DFT computational methods to understand the effect of alkyl groups in governing the basic structural and electronic aspects of BODIPY dyes. As demonstrated in Chapter 4 and Chapter 5, apparently electronically inactive alkyl groups can be of immense importance to control the overall photophysics of BODIPYs. In this context, a systematic strategy su was utilized considering all possible outcomes of constitutionally-isomeric molecules to understand the effects of alkyl groups on the BODIPY molecules. Four different computational methods were employed to ascertain the unanimity of the observed trends associated with the molecular properties. In line with experimental observations, it was found that alkyl substituents in BODIPY dyes situated at 3/5-positions effectively participate in stabilization as well as planarization of such molecules. Screening of all the possible isomeric molecular systems was used to understand the individual properties and overall effects of the typical alkyl substituents in controlling several basic properties of such BODIPY molecules.

This book examines polarity sensitivity—a ubiquitous phenomenon involving expressions such as anybody, nobody, ever, never, and somebody and their counterparts in other languages, with particular focus on Arabic. These expressions belong to different classes such as negative and positive polarity, negative concord, and negative indefinites, which led to examining their syntax and semantics separately. In this book, Ahmad Alqassas pursues a unified approach that relies on examining the interaction between the various types of polarity sensitivity. Treating this interaction is fundamental for scrutinizing their licensing conditions. Alqassas draws on data from Standard Arabic and the major regional dialects represented by Jordanian, Egyptian, Moroccan, and Qatari. The book provides a new perspective on the syntax–semantic interface and develops a unified syntactic analysis for polarity sensitivity. Through the (micro)comparative approach, Alqassas explains the distributional contrasts with a minimal set of universal syntactic operations such as Merge, Move, and Agree, and a fine-grained inventory of negative formal features for polarity items and their licensors. The features are simple invisibles that paint a complex landscape of polarity. The results suggest that syntactic computation of Arabic polarity (externally merged in the left periphery) is subservient to the conceptual–intentional interface. Alqassas argues for last resort insertion of covert negation operators in the CP layer to interpret non-strict NCIs, which is an extra mechanism that serves the semantic interface but adds to the complexity of syntactic computation. Likewise, head NPIs in the left periphery require licensing by operators higher than the tense phrase, adding more constraints on the syntactic licensing.

Present work proposes approach that significantly shortens the calculation time for NPSH(r). This time is comparable with time for the head calculations. Most cavitation models take into account phase change, bubble dynamics, turbulent pressure fluctuations, etc. In this case multiphase flow model must be used. This work presents some simplifications, based on the physical nature of cavitation on the pump impeller, which significantly (10–50 times) reduces the calculation time of NPSH (r). The main idea of proposed procedure is to determine the liquid vapor (cavitation) zone simply from steady state calculation of one phase incompressible flow without taking into account multiphase effects. Based on absolute pressure distribution it is easy to determine areas with absolute pressure lower then saturated liquid vapor pressure for given liquid conditions. Consequently it is possible to consider the steady state location of liquid vapor (cavitation) on the impeller vanes. So this zone may simply be expelled from the flow domain. For many pump related cases, these zones are very close to cavitation areas, and give main impact on the head of the pump. Commercial Fluent 12.1.4 code is used for calculations. Proposed procedure for NPSH(r) calculation is in good agreement with test data for different types of pumps and may be used as a tool to shorten a design process for new pumps.

Indira Gandhi Centre for Atomic Research for their Fast Breeder Reactor had a requirement of two primary sodium pumps, with relatively medium head and comparatively large flow rate. The pumps had to be vertical bowl type, with inverted suction, drawing the relatively cold liquid sodium from the reactor pool, and forcing it over the fuel rods. The flow involved was 4.3 M3/sec. per pump and the head involved was 75 m. The available NPSH was 16.02m. The choice of the right speed was the first hurdle to be overcome. The size of the pump governed the cost of the reactor. Hence it was essential to make the pump as compact as practicable, by designing it to run at the highest possible speed. On the other hand the required NPSH of the pump increased with speed, there by reducing the safety cushion between required NPSH and available NPSH. Increasing the available NPSH beyond 15.55 m to accommodate higher speeds also increased the cost of the reactor phenomenally. Coupled with the requirement of head, flow rate, efficiency, the application demanded a certain erosion life of the pump impeller. Concluding from the previous experience and available literature on the subject, it was necessary to limit the size of the cavitation bubble patch, during operation under available NPSH, to meet erosion life requirement. The paper describes how the choice of speed was made and what were the criteria applied for deciding the value of 3% head drop NPSH. It also describes how a closed circuit test rig was installed for the purpose of testing a model pump and how the usual performance and NPSHR tests paint erosion tests and visual cavitation tests were carried out on a geometrically similar, smaller model pump, to decide that the prototype pump built from the model will meet all the requirements of head, flow rate, efficiency, 3% head drop NPSHR, 0% head drop NPSHR, Paint erosion NPSHR, and the cavitation patch size to meet desired erosion life criteria, in the laboratories of Kirloskar Brothers Limited.

Cavitation is often linked to the inability of the system to provide sufficient NPSH to the pump. Pump users often feel safe running a pump if the NPSH required by the pump is below what is available in the system. What is gas entrainment within process fluid and how does it affect pump performance? Is there a connection of entrained gas with cavitation? When flow through the pump is too low, a part of the mechanical energy that is put in for running the pump is converted to pressure energy and the remaining goes to heat the liquid. This raises the liquid temperature and eventually vaporizes it. This vapor stays within the process liquid as bubbles, which causes cavitation. All the above conditions cause cavitation. This paper describes how these conditions develop, and shows how to identify and then rectify them.

The recent worldwide epidemic of Covid-19 disease, for which there is no vaccine or medications to prevent or cure it, led to the adoption of public health measures by governments and populations in most of the aected countries to avoid the contagion and its spread. These measures are known as nonpharmaceutical interventions (NPIs) and their implementation clearly produces social unrest as well as aects the economy. Frequently, NPIs are implemented with an intensity quantied in an ad hoc manner. Control theory oers a worthwhile tool for determining the optimal intensity of the NPIs in order to avoid the collapse of the healthcare system while keeping them as low as possible, yielding in a policymakers concrete guidance. We propose here the use of a simple proportional controller that is robust to large parametric uncertainties in the model used.

A numerical analysis is performed to assess the capability of common simulation methods, in particular Ansys CFX, to predict the performance and NPSH curve of a centrifugal pump at very low specific speed for both, design and off-design conditions. In all cases, we use an entire numerical model containing the impeller, the volute casing, the side chambers as well as suction pipe and pressure pipe. A three-dimensional setup is used, testing the following numerical models: steady, i.e. frozen rotor model, unsteady model accounting for the impeller movement and the relative impeller-volute position, single-phase flow as well as cavitating flow conditions. The global performance of the pump is assessed in terms of pressure head, power consumption and pump efficiency for single-phase flow. Furthermore, the drop of the pump head and Net Positive Suction Head (NPSH) characteristics are analyzed for cavitating flow conditions. Numerical results are validated against experimental data. Regarding non-cavitating flow conditions, the trend of the characteristic curves is well predicted, while absolute performance values differ from measured data significantly. The results of steady and unsteady calculations deviate from each other by less than 2%. Concerning cavitating flow, unsteady simulations have to be performed in particular for overload conditions, in order to obtain convergence of the solver. The trend of the measured NPSH curve is well captured with default cavitation model parameters. For nominal and overload, the predicted NPSH curve underestimates the measured one significantly.

The primary function of an aero engine fuel system is to supply metered fuel to the combustion chamber at all operating conditions based on the flow demand set by the engine controller. Centrifugal pump is one of the components in fuel system that feeds fuel to the HP pump. Impeller design is a critical one which dictates the overall performance of centrifugal pump. This paper discusses about design and performance evaluation of impeller with twisted blade configuration. Impeller design is performed based on Euler’s one dimensional theory. Steady state performance of the impeller at design and off-design operating conditions is analyzed by using commercial CFD code ANSYS-CFX with a standard SST turbulence model. The governing mathematical model for flow analysis is a three dimensional incompressible Reynolds Averaged Navier-Stokes (RANS) equation. Cavitation phenomenon is simulated in the CFD multiphase analysis to assess the pump impeller performance under cavitation at different NPSH values. Rayleigh-Plesset cavitation model is used along with RANS equation to perform cavitation analysis. From this study, the simulation method and technique adapted is appropriate for predicting the performance of impeller of centrifugal pump with or without cavitation. Performance of the impeller reduces drastically as there is decrease in NPSH. The prediction of critical NPSH is vital for safer operation of the pump, specifically at high altitude the pump inlet pressure falls which may result in cavitation during operation.

To study the cavitation flow field and cavitation induced noise features in a centrifugal pump, a model pump is chosen as the research object. Cavitation flow field at design and off-design operating conditions is visualized by high speed camera. The cavitation bubbles spatial distribution changing with pump net positive suction head (NPSH) value have been captured. Meanwhile, cavitation noise signals from the pump at the corresponding operating conditions have been acquired in the frequency band from 10 up to 8kHz. Noise levels at broadband frequency and discrete frequency, such as rotating frequency (RF) and blade pass frequency (BPF), are discussed. It is of help to recognize the relationship between cavitation bubbles and emitted noise spectrum characteristics. Experimental results indicate that the total noise level is unlikely to raise before and in the cavitation inception period. But sound pressure level (SPL) over high frequency broadband increases obviously, as well as SPL at BPF and half of that. It is hard to change at RF. When the NPSH goes down until to the onset of cavitation damage, cavitation cloud appears. The volume fraction of bubbles in every impeller passage is different. The total and high frequency noise level reach peak values near the NPSH critical point. The discrete tone at half of BPF also raises steeply. Cavitation bubbles are filled both on suction and pressure side of the blades in fully developed cavitation stage. Emitted noise energy fluctuates due to the unsteady features of internal flow in the pump.

Until a vaccine is widely available, face masks and other nonpharmaceutical interventions (NPIs) will continue to be the frontline defense against Covid-19 in developing countries. But their effectiveness depends critically on compliance by young adults, who are most likely both to become infected and to infect others. We conducted a randomized controlled trial in Bogotá, Colombia, to assess the effectiveness of informational nudges on university students concern about Covid-19, recent compliance with NPI recommendations, and intended future compliance. Although nudges boosted concern, they had limited effects on either recent or intended future compliance. We attribute these null results to high baseline levels of information about and compliance with NPIs an informational diminishing returns scenario that is likely to be increasingly common globally. Nudges were more effective at boosting recent compliance among participants who were politically left-wing, were relatively poor, and lived with more people.

Nudges boosted concern about COVID-19 but had limited effects on either recent compliance or intended future compliance with recommendations from nonpharmaceutical interventions (NPIs). These null results were probably due to participants high baseline levels of information about and compliance with NPIsan informational diminishing returns scenario that is likely to be increasingly common globally. Nudges increased recent compliance among participants who were politically left-wing, were relatively poor, and lived with more people.