Experimental Study on the Role of Entropy Waves in Low-Frequency Oscillations in a RQL Combustor

2004 ◽  
Vol 128 (2) ◽  
pp. 264-270 ◽  
Author(s):  
J. Eckstein ◽  
E. Freitag ◽  
C. Hirsch ◽  
T. Sattelmayer
Keyword(s):  
Experimental Study ◽  
Low Frequency ◽  
Feedback Mechanism ◽  
Mean Flow ◽  
Primary Zone ◽  
Start Up ◽  
Atomization Characteristics ◽  
Aero Engines ◽  
The Impact

“Rumble” is a self-excited combustion instability, usually occurring at the start-up of aero-engines with fuel-spray atomizers at sub-idle and idle conditions, and exhibiting low limit frequencies in the range of 50Hzto150Hz. Entropy waves at the (nearly) choked combustor outlet are supposed to be the key feedback mechanism for the observed self-excited pressure oscillations. The experimental study presented here aims at clarifying the role of entropy waves in the occurrence of rumble. A generic air-blast atomizer with a design prone to self-excitation has been incorporated into a thermoacoustic combustor test rig with variable outlet conditions. The thermoacoustic response of the flame was characterized by recording the OH* chemiluminescence, the dynamic pressures, the dynamic temperatures, and by applying PIV. The measurements have shown the occurrence of periodic hot spots traveling with the mean flow with considerable dispersion. Measurements have been conducted with an open-ended resonance tube in order to eliminate the impact of entropy waves on the mechanism of self-excitation. The oscillation obtained, comparable in amplitude and frequency, proved that self-excitation primarily depends on convective time delays of the droplets in the primary zone and thus on the atomization characteristics of the nozzle.

Experimental Study on the Role of Entropy Waves in Low-Frequency Oscillations for a Diffusion Burner

2004 ◽  
Author(s):  
J. Eckstein ◽  
E. Freitag ◽  
C. Hirsch ◽  
T. Sattelmayer
Keyword(s):  
Experimental Study ◽  
Low Frequency ◽  
Feedback Mechanism ◽  
Mean Flow ◽  
Primary Zone ◽  
Start Up ◽  
Atomization Characteristics ◽  
Aero Engines ◽  
The Impact

“Rumble” is a self-excited combustion instability, usually occurring at the start-up of aero-engines with fuel-spray atomizers at sub-idle and idle conditions, and exhibiting low limit frequencies in the range of 50 Hz to 150 Hz. Entropy waves at the (nearly) choked combustor outlet are supposed to be the key feedback-mechanism for the observed self-excited pressure oscillations. The experimental study presented here aims to clarify the role of the entropy waves for the occurrence of rumble. A generic air-blast atomizer with a design being prone to self-excitation has been incorporated into a thermoacoustic combustor test rig with variable outlet conditions. The flame thermoacoustics were characterized by recording the OH*-chemiluminescence, the dynamic pressures, the dynamic temperatures, and by applying PIV. The measurements have shown the occurrence of periodic hot spots travelling with the mean flow with considerable dispersion. Measurements have been conducted with an open-ended resonance tube in order to eliminate the impact of entropy waves on the mechanism of self-excitation. The oscillation obtained, comparable in amplitude and frequency, proved that self-excitation primarily depends on convective time delays of the droplets in the primary zone and thus on the atomization characteristics of the nozzle.

scholarly journals TET2 mutations as a part of DNA dioxygenase deficiency in myelodysplastic syndromes

2021 ◽  
Author(s):  
Carmelo Gurnari ◽  
Simona Pagliuca ◽  
Yihong Guan ◽  
Vera Adema ◽  
Courtney E Hershberger ◽  
...  
Keyword(s):  
Myelodysplastic Syndromes ◽  
Prognostic Significance ◽  
Age Groups ◽  
Feedback Mechanism ◽  
Dna Demethylation ◽  
Compensatory Mechanisms ◽  
Poor Outcomes ◽  
Relationship Of ◽  
The Impact

Decrease in DNA dioxygease activity generated by TET2 gene family is crucial in myelodysplastic syndromes (MDS). The general down-regulation of 5-hydroxymethylcytosine (5-hmC) argues for a role of DNA demethylation in MDS beyond TET2 mutations, which albeit frequent, do not convey any prognostic significance. We investigated TETs expression to identify factors which can modulate the impact of mutations and thus 5-hmC levels on clinical phenotypes and prognosis of MDS patients. DNA/RNA-sequencing and 5-hmC data were collected from 1,665 patients with MDS and 91 controls. Irrespective of mutations, a significant fraction of MDS patients exhibited lower TET2 expression, while 5-hmC levels were not uniformly decreased. In searching for factors explaining compensatory mechanisms, we discovered that TET3 was up-regulated in MDS and inversely correlated with TET2 expression in wild-type cases. While TET2 was reduced across all age-groups, TET3 levels were increased in a likely feedback mechanism induced by TET2 dysfunction. This inverse relationship of TET2 and TET3 expression also corresponded to the expression of L-2-hydroxyglutarate dehydrogenase, involved in agonist/antagonist substrate metabolism. Importantly, elevated TET3 levels influenced the clinical phenotype of TET2-deficiency whereby the lack of compensation by TET3 (low TET3 expression) was associated with poor outcomes of TET2 mutant carriers.

The Role of Extratropical Air–Sea Interaction in the Autumn Subseasonal Variability of the North Atlantic Oscillation

2019 ◽  
Vol 32 (22) ◽  
pp. 7697-7712 ◽  
Author(s):  
Yu Nie ◽  
Hong-Li Ren ◽  
Yang Zhang
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Gulf Stream ◽  
Low Frequency ◽  
Mean Flow ◽  
The North ◽  
Subseasonal Variability ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract Considerable progress has been made in understanding the internal eddy–mean flow feedback in the subseasonal variability of the North Atlantic Oscillation (NAO) during winter. Using daily atmospheric and oceanic reanalysis data, this study highlights the role of extratropical air–sea interaction in the NAO variability during autumn when the daily sea surface temperature (SST) variability is more active and eddy–mean flow interactions are still relevant. Our analysis shows that a horseshoe-like SST tripolar pattern in the North Atlantic Ocean, marked by a cold anomaly in the Gulf Stream and two warm anomalies to the south of the Gulf Stream and off the western coast of northern Europe, can induce a quasi-barotropic NAO-like atmospheric response through eddy-mediated processes. An initial southwest–northeast tripolar geopotential anomaly in the North Atlantic forces this horseshoe-like SST anomaly tripole. Then the SST anomalies, through surface heat flux exchange, alter the spatial patterns of the lower-tropospheric temperature and thus baroclinicity anomalies, which are manifested as the midlatitude baroclinicity shifted poleward and reduced baroclinicity poleward of 70°N. In response to such changes of the lower-level baroclinicity, anomalous synoptic eddy generation, eddy kinetic energy, and eddy momentum forcing in the midlatitudes all shift poleward. Meanwhile, the 10–30-day low-frequency anticyclonic wave activities in the high latitudes decrease significantly. We illustrate that both the latitudinal displacement of midlatitude synoptic eddy activities and intensity variation of high-latitude low-frequency wave activities contribute to inducing the NAO-like anomalies.

scholarly journals Key determinants of organisational silence for non-standard workers

2016 ◽  
Vol 54 (6) ◽  
pp. 1522-1538 ◽  
Author(s):  
Willam Joseph Pirie
Keyword(s):  
Life Cycle ◽  
Academic Research ◽  
Limited Liability ◽  
Future Contract ◽  
Structured Interviews ◽  
Diverse Range ◽  
Content Type ◽  
Start Up ◽  
The Impact

Purpose – The purpose of this paper is to identify the key determinants of organisational silence from the perspective of non-standard workers (NSWs). The study focuses on three research themes: first, analysing the experiences motivating NSWs to remain silent; second, analysing the role of the NSW life cycle in the motivation to remain silent, the final theme is evaluation of the impact on organisational voice of an organisation employing a workforce in which NSWs and standard workers (SWs) are blended. Design/methodology/approach – The study utilises a phenomenological approach, as defined by Van Manen (2007), to collect and analyse the phenomenon of organisational silence from the perspective of NSWs. The NSWs are defined as individuals operating via Limited Liability UK registered companies created for the purpose of delivering services to organisations via a contract of services. This study employed a combination of phenomenology and hermeneutics to collect and analyse the data collected from the NSWs using semi-structured interviews (Lindseth and Norberg, 2004). Findings – The study concludes with three core findings. NSWs experience similar motivational factors to silence as experienced by standard workers (SWs). The key differential between a SW and a NSW is the role of defensive silence as a dominant motivator for a start-up NSW. The study identified that the reasons for this is that new NSWs are defensive to protect their reputation for any future contract opportunities. In addition, organisations are utilising the low confidence of new start up NSWs to suppress the ability of NSWs to voice. The research indicates how experienced NSWs use the marketing stage of their life cycle to establish voice mechanisms. The study identified that NSWs, fulfiling management and supervisory roles for organisations, are supporting/creating climates of silence through their transfer of experiences as SWs prior to becoming NSWs. Research limitations/implications – This study is a pilot study, and the findings from this study will be carried forward into a larger scale study through engagement with further participants across a diverse range of sectors. This study has identified that there is a need for further studies on organisational silence and NSWs to analyse more fully the impact of silence on the individuals and the organisation itself. A qualitative phenomenological hermeneutical study is not intended to be extrapolated to provide broad trends. The focus of the phenomenological hermeneutic research methodology is on describing and analysing the richness and depth of the NSW’s experiences of silence in organisational settings. Originality/value – This paper draws together the studies of worker classification, motivators for organisational silence, and the impact of blending SWs and NSWs in an organisational setting. The study demonstrates that academic research to date has focused predominantly on SWs to the exclusion of the 1.5 million, and growing, NSWs in the UK. This study examines these under-represented workers to analyse the participants’ experiences of organisational silence, and its consequences in organisational settings, demonstrating a need for further studies.

scholarly journals Gamification in e-learning: The mitigation role in technostress

2021 ◽  
Vol 10 (2) ◽  
pp. 606
Author(s):  
Faridiah Aghadiati Fajri ◽  
RY. Kun Haribowo P. ◽  
Nurisqi Amalia ◽  
Dina Natasari
Keyword(s):  
Technology Implementation ◽  
Feedback Mechanism ◽  
User Resistance ◽  
Face To Face ◽  
Digital World ◽  
Business Applications ◽  
Quasi Experimental ◽  
E Learning ◽  
The Impact

The digital world demands graduates who are accustomed to deal with technology. Blended learning is one of the strategies by combining online media with face-to-face classes. It cannot be denied that students who interact with technology experience stress and tension. This condition have an impact on the learning process so that a way out is needed to bring it down. Gamification is a gaming technique that is applied to non-game applications to increase pleasure when interacting with these applications. This feature has been implemented in business applications, social media, e-commerce, and e-learning. However, the impact of playfulness in mitigating technostress has not been studied. This research examined the role of feedback mechanism and presentation mechanism in giving pleasure in LMS. Furthermore, this playfulness is expected to reduce the stress experienced by users. The research was conducted using a quasi-experimental method by giving participants time to follow the course with the gamification feature. The results showed that the gamification mechanism is able to provide pleasure which in turn will reduce the user's stress level. Based on the user-perceived of playfulness, gamification can reduce stress levels so it will reduce user resistance and increase the effectiveness of technology implementation.

scholarly journals The Role of Nurturing Technopreneurship Education and Building University Students’ Entrepreneurial Mindsets and Skill Sets in Fostering Digital Innovation and Augmenting the Tech Start-Up Ecosystem in Bahrain

2021 ◽  
Vol 20 (6) ◽  
pp. 152-173
Author(s):  
Sama’a Al Hashimi ◽  
Yasmina Zaki ◽  
Ameena Al Muwali ◽  
Nasser Mahdi
Keyword(s):  
Higher Education ◽  
Creative Thinking ◽  
Educational Background ◽  
Entrepreneurial Success ◽  
Support Organizations ◽  
Start Up ◽  
The Government ◽  
The Right ◽  
The Impact

This paper examines the relationship between the success of tech start-ups and the educational backgrounds of their owners. To better comprehend and encourage technopreneurial growth, it is essential to understand the educational background of tech start-up founders in Bahrain. The paper attempts to explore whether or not different educational qualifications of tech start-up founders are associated with their success. It also aims to investigate the pedagogical approaches, strategies, skills, and objectives that may have contributed to the success of leading technopreneurs, locally and globally in an effort to suggest the right practices to implement in Bahrain in order to emulate their educational experiences. The research qualitatively investigates the perceptions and academic experiences of the founders of five innovative Bahraini digital applications in an attempt to explore the role of their education in their success and growth. In addition, twelve support organizations in Bahrain were interviewed to examine the influence of higher education on entrepreneurial success. The paper argues that education is very essential to entrepreneurial success, and its findings provide clear evidence of the impact of education which focuses on fostering creative thinking, innovation, and team-working skills on technopreneurial success. These findings may have implications for universities in Bahrain to promote successful entrepreneurs through integrating the best practices in innovation and entrepreneurship education into the curriculum, and strengthening their cooperation with the government and various support organizations. Finally, the paper provides higher education institutions with guidelines and recommendations to maximize their role in the tech start-up ecosystem in Bahrain.

scholarly journals Laminar buffet and flow control

2019 ◽  
Vol 234 (1) ◽  
pp. 124-139 ◽  
Author(s):  
V Brion ◽  
J Dandois ◽  
R Mayer ◽  
P Reijasse ◽  
T Lutz ◽  
...  
Keyword(s):  
Shock Wave ◽  
Separation Bubble ◽  
Control Strategies ◽  
Three Dimensional ◽  
Low Frequency ◽  
Frequency Component ◽  
High Frequency Component ◽  
Mean Flow ◽  
Flow Past ◽  
The Impact

An experimental investigation of the transonic flow past the laminar OALT25 airfoil has been conducted to analyze the impact of laminar flow upon the shock wave dynamics and the existence of a laminar buffet like phenomenon. Tests have been carried out at freestream Mach numbers varying in the range of 0.7–0.8, angle of attack from 0.5° to 4°, and with two tripping configurations at the upper surface of the wing. The (airfoil) chord based Reynolds number is about three million. Results obtained from pressure taps and sensors measurements, as well as Schlieren visualizations of the flow reveal the presence of a laminar buffet phenomenon in sharp contrast with the turbulent phenomenon, as it features a freestream- and chord-based normalized frequency of about unity while turbulent buffet occurs for a frequency close to 0.07 (Jacquin et al., AIAA J 2009; 47). A low-frequency mode, at a frequency of about 0.05 is also present in the laminar situation, notably lower than the high-frequency component. The latter exhibits strong oscillations of the shock foot and vertical wavelike deformations of the shock wave and the former moves the shock back and forth over a small portion of chord, quite similar to the turbulent phenomenon. The mean flow past the laminar wing is characterized by a laminar separation bubble under the shock foot, which likely contributes much to the novel dynamics revealed by the present experiments. Two control strategies of the unsteady shock wave are implemented, one consisting of three-dimensional bumps and one consisting of steady jets blowing transversely to the freestream. It is found that bumps provide a significant reduction of the buffet intensity in the laminar situation. The jets are able to completely remove the flow unsteadiness in both laminar and turbulent conditions.

The impact of entrepreneurship education on innovative start-up intention: the mediating role of entrepreneurial mind-sets

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Rami Hanandeh ◽  
Sakher M.A. Alnajdawi ◽  
Ammar Almansour ◽  
Hamzah Elrehail
Keyword(s):  
University Students ◽  
Educational Institution ◽  
Entrepreneurship Education ◽  
The Body ◽  
Equation Modeling ◽  
Content Type ◽  
Mediating Role ◽  
Start Up ◽  
The Impact

PurposeEntrepreneurship education at universities aims to create entrepreneurial thinking and spread the culture of entrepreneurial awareness, skills and attitudes to students to stimulate their entrepreneurship intentions as graduates. This study investigates the impact of entrepreneurship education on innovative start-up intention as well as the mediating role of entrepreneurial mind-sets of university students.Design/methodology/approachStructural equation modeling (SEM) was used for analysis with (n = 204) valid questionnaires collected from university students.FindingsThe main findings show that entrepreneurial mind-sets mediate the relationship between entrepreneurship education and innovative start-up intention.Originality/valueThis study contributes to the body of knowledge by its application in a higher educational institution and enriches the literature with new evidence that entrepreneurship education could enhance innovative start-up intention.

CSR types and the moderating role of corporate competence

2018 ◽  
Vol 52 (7/8) ◽  
pp. 1358-1386 ◽  
Author(s):  
Xiaoye Chen ◽  
Rong Huang ◽  
Zhiyong Yang ◽  
Laurette Dube
Keyword(s):  
Experimental Study ◽  
Repeated Measures ◽  
Empirical Studies ◽  
Interactive Effects ◽  
Survey Study ◽  
Content Type ◽  
Different Types ◽  
The Impact ◽  
Moderating Role

PurposeThis paper aims to investigate the impact of different types of corporate social responsibility (CSR; i.e. value-creating CSR, promotional CSR and philanthropic CSR) on consumer responses and the moderating role of corporate competence.Design/methodology/approachThe authors tested the hypotheses by using two empirical studies – a survey and an experimental study. The evidence is generated based on generalized linear model repeated-measures ANOVAs for the survey study and two-way factorial ANOVAs for the experimental study.FindingsThe findings show that in general, consumers respond to value-creating CSR more favorably than to philanthropic CSR or promotional CSR. In addition, corporate competence moderates consumers’ responses to different types of CSR in such a way that promotional CSR is more likely to have the desired effects when carried out by low-competency rather than by high-competency firms, whereas value-creating CSR is more effective for high-competency firms than for low-competency ones. Philanthropic CSR works equally in both types of firms.Research limitations/implicationsThis research answers a long-term call to study the differential consumer effects of various CSR types. It also identifies perceived corporate competence, an important consumer-based corporate factor, as a potential moderator of consumers’ response to CSR types.Practical implicationsArmed with the findings, companies can choose CSR practices that fit with their company characteristics. This research offers important and specific managerial implications to firms with different company profiles on their CSR choices.Originality/valueGiven that today’s managers are faced with the challenge of selecting desirable CSR activities from a group of options, the authors answered the call by studying the differential effects of a wide array of CSR choices and provide important practical guidance to managers. For the first time in the literature, the study also investigates the potential interactive effects between specific CSR types and corporate competence on consumer reactions. This inquiry bears significant relevance to the ongoing discussions concerning whether and how company characteristics generate influences on the outcomes of CSR strategies.

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