Subcritical Research Articles

Transforming Aviation's Impact on the Climate: Rethinking the Research Strategy.

Aviation is under tremendous pressure to mitigate its impacts on the climate, but the best response strategies are unknown today due to deep uncertainties. How low-emission fuels will scale to levels relevant for the industry, along with the best strategies for managing contrails and other non-CO2 effects, are unknowable today with unknown cost and disruption. A conventional risk-based approach that involves investment across a known set of options is unworkable; instead, we argue that an experimentalist approach is needed that addresses deep uncertainties head on. This hinges on four key factors: a critical mass of actors facing strong incentives to identify solutions, a wide search for alternatives through experiments, periodic assessments, and adjustment of goals and strategies. Present strategies do not give enough attention to higher-risk alternatives with disruptive potential, because those approaches have few political and organizational supporters. Small groups of highly motivated actors─such as the nascent coalition of first movers on clean aviation already forming in Europe and the U.S.─could initiate an experimentalist program. The challenges of the aviation sector mirror other hard-to-abate sectors, making this framework potentially applicable to a wider set of sectors where technological, business, and investment choices are shrouded in deep uncertainty.

Board gender diversity (BGD): compelling evidence in support for the critical mass theory

PurposeThe paper aims to identify the level of support and expand on the issues recently raised in the literature concerning critical mass theory and board gender diversity (BGD).Design/methodology/approachThe authors systematically searched relevant articles on the Scopus database in March 2024, identifying 132 articles. After removing book chapters, conference papers and reviews, the number was reduced to 122. An additional 16 were discarded as they were irrelevant (e.g. political, theoretical or conceptual) to the current study, leaving a final sample of 106 articles. This longitudinal study covers the period from 2016 to 2024.FindingsThe paper finds compelling evidence supporting the critical mass theory and underscores the importance of corporate BGD in today’s society. It also offers explanations for the few cases where critical mass theory may not be fully supported. It highlights that the performance benefits of corporate BGD, in many cases, only exist when there is a critical mass of female directors on the board.Practical implicationsIt lends support to policymakers in pursuing corporate BGD through quotas, provided that the incentive is not just to fill the numbers.Originality/valueThe paper offers a unique perspective on the level of support for the critical mass theory. It is believed to be the first paper to conduct a longitudinal study to investigate the support for the critical mass theory.

Empowering Women to Lead Cybersecurity: The Effect of Female Executives on Disclosure Sentiment

ABSTRACTThis study investigates the impact of gender diversity (i.e., the presence of female executives on corporate boards) on the sentiment of cybersecurity information disclosure, including its likelihood, magnitude, and tone. We develop a unique dataset providing an extensive view of the development and evolution of cybersecurity‐related disclosure practices among prominent publicly traded US companies over a 19‐year period (2002–2020). We find strong evidence that female executives are more likely to disclose, and they report significantly more cybersecurity‐related information compared to their male counterparts. Additionally, female executives adopt a more conservative, uncertain, and litigious tone in their cybersecurity disclosures than male executives. The results also support the notion of a critical mass of female executives on the board and align with various theories, emphasising the importance of gender diversity in promoting high‐quality cybersecurity disclosure practices within firms. Furthermore, we examine several channels contributing to the heterogeneity of cybersecurity disclosures between female and male executives, and consider the effects of the black swan events (i.e., the financial crisis and the COVID‐19 pandemic).

THE COOLING EFFECT OF COMBUSTOR EXIT LOUVER SCHEME ON A TRANSONIC NOZZLE GUIDE VANE ENDWALL

Abstract The ever-increasing combustor exit temperature in modern turbine engine designs raises challenges for the nozzle guide vane cooling. Due to the complexity of NGV cooling design, the cooling effect from the upstream combustor cooling features can prove valuable. This study investigates, experimentally and numerically, the cooling effect of a louver cooling scheme near the combustor exit on the NGV endwall. The wind tunnel testing and CFD simulation are carried out with engine-representative conditions of an exit Mach number of 0.85, an exit Reynolds number of 1.5 × 106, an inlet turbulence intensity of 16%, and a density ratio of 2.1. Various coolant mass flow ratios from 1% to 4% are tested to demonstrate the effect of the coolant rate. For the geometry studied, the results found a critical mass flow ratio between 1%~2%. The coolant forms a uniform film only by exceeding this value to provide good coverage upstream of the NGV passage inlet. As for the cooling of the NGV passage, the mass flow ratio of the range investigated is insufficient for desirable cooling performance. The pressure side endwall proves most difficult for the coolant to reach. In addition, the fishmouth cavity at the combustor-NGV passage causes a three-dimensional cavity vortex that transports the coolant in the pitch-wise direction. The transport pattern is dependent on the coolant mass flow ratio. Therefore, the authors propose combining this louver scheme with the upstream jump cooling scheme for a desirable NGV cooling system.

Commit: Online Groups with Participation Commitments

In spite of efforts to increase participation, many online groups struggle to survive past the initial days, as members leave and activity atrophies. We argue that a main assumption of online group design---that groups ask nothing of their members beyond lurking---may be preventing many of these groups from sustaining a critical mass of participation. In this paper, we explore an alternative commitment design for online groups, which requires that all members commit at regular intervals to participating, as a condition of remaining in the group. We instantiate this approach in a mobile group chat platform called Commit, and perform a field study comparing commitment against a control condition of social psychological nudges with N=57 participants over three weeks. Commitment doubled the number of contributions versus the control condition, and resulted in 87% (vs. 19%) of participants remaining active by the third week. Participants reported that commitment provided safe cover for them to post even when they were nervous. Through this work, we argue that more effortful, not less effortful, membership may support many online groups.

Current challenges and threats to the implementation of social policy under the conditions of marital state

The problems of the implementation of social policy are currently determined by the accumulated problem of the unreformed sector of the social sphere and the extremely negative impact of the martial law, which leads to an increase in the critical mass of people who need social assistance and effective solutions that can contribute to the implementation of social policy in accordance with current challenges and threats. This article focuses on identifying and structuring current challenges and threats to the implementation of social policy under martial law. It is established that, given the longterm nature of martial law, social policy is currently under the critical influence of pre2022 problems, which are exacerbated by a large-scale invasion, and the structuring of current challenges and threats that are characteristic of the current state of social policy implementation, given martial law, is an important and relevant topic for research. After all, today the issue of clearly fixing and structuring the current challenges and threats to the implementation of social policy in the conditions of martial law is acute. The purpose of the article is to define and structure the current challenges and threats to the implementation of the social sphere in the conditions of martial law. In the process of research, it was established that in today’s conditions, the implementation of social policy has significant limitations and barriers. Four groups of institutional restrictions are identified, which include the inconsistency of the legal framework; bureaucratic obstacles; insufficient coordination between various state authorities; low level of professional training of social workers. Three groups of obstacles to the effective implementation of social policy are also highlighted, namely: economic, political, and corruption. The main types of threats are identified, including: financial, social, technical and security, each of which creates a whole range of challenges. The following challenges have a high priority to be taken into account in the implementation of social policy: the problem of the state budget deficit, dependence on international donors, the increase in the number of people who need social protection, the decrease in the standard of living and the provision of housing, the further course of military operations and their intensity, internal instability. It was established that further research should be focused on finding effective tools that will allow, taking into account the existing risks and threats, to develop appropriate mechanisms for minimizing the identified threats and challenges for the effective implementation of social policy as quickly as possible.

Tetraquarks made of sufficiently unequal-mass heavy quarks are bound in QCD

Tetraquarks, bound states composed of two quarks and two antiquarks, have been the subject of intense study but are challenging to understand from first principles. We apply variational and Green’s function Monte Carlo methods to compute tetraquark ground-state energies in potential nonrelativistic QCD using a wide range of color and spatial wave functions. We find no evidence for bound tetraquarks composed of equal-mass quarks and antiquarks. Conversely, we find clear evidence for the existence of bound tetraquarks for sufficiently unequal quark/antiquark mass ratios at all overall mass scales where our effective theory results are applicable. We predict the critical mass ratios for bound state formation and study tetraquark bound states’ spatial and color structure at leading order and next-to-leading order in potential nonrelativistic QCD. Published by the American Physical Society 2024

Occurrence of Gravitational Collapse in the Accreting Neutron Stars of Binary-driven Hypernovae

The binary-driven hypernova (BdHN) model proposes long gamma-ray bursts (GRBs) originate in binaries composed of a carbon–oxygen (CO) star and a neutron star (NS) companion. The CO core collapse generates a newborn NS and a supernova that triggers the GRB by accreting onto the NSs, rapidly transferring mass and angular momentum to them. This article aims to determine the conditions under which a black hole (BH) forms from NS collapse induced by the accretion and the impact on the GRB’s observational properties and taxonomy. We perform three-dimensional, smoothed particle hydrodynamics simulations of BdHNe using up-to-date NS nuclear equations of state, with and without hyperons, and calculate the structure evolution in full general relativity. We assess the binary parameters leading either NS in the binary to the critical mass for gravitational collapse into a BH and its occurrence time, t col. We include a nonzero angular momentum of the NSs and find that t col ranges from a few tens of seconds to hours for decreasing NS initial angular momentum values. BdHNe I are the most compact (about 5 minute orbital period), promptly form a BH, and release ≳1052 erg of energy. They form NS–BH binaries with tens of kiloyears merger timescales by gravitational-wave emission. BdHNe II and III do not form BHs, and release ∼1050–1052 erg and ≲1050 erg of energy, respectively. They form NS–NS binaries with a range of merger timescales larger than for NS–BH binaries. In some compact BdHNe II, either NS can become supramassive, i.e., above the critical mass of a nonrotating NS. Magnetic braking by a 1013 G field can delay BH formation, leading to BH–BH or NS–BH with tens of kiloyears merger timescales.

Theory of Turbulent Equilibrium Spheres with Power-law Linewidth–Size Relation

Dense cores inherit turbulent motions from the interstellar medium in which they form. As a tool for comparison to both simulations and observations, it is valuable to construct theoretical core models that can relate their internal density and velocity structure while predicting their stability to gravitational collapse. To this end, we solve the angle-averaged equations of hydrodynamics under two assumptions: (1) the system is in a quasi-steady equilibrium; (2) the velocity field consists of radial bulk motion plus isotropic turbulence, with turbulent dispersion increasing as a power law in the radius. The resulting turbulent equilibrium sphere (TES) solutions form a two-parameter family, characterized by the sonic radius r s and the power-law index p. The TES is equivalent to a Bonnor–Ebert (BE) sphere when r s → ∞ . The density profile in the outer regions of the TES is slightly shallower than the BE sphere, but is steeper than the logotropic model. Stability analysis shows that the TESs with size exceeding a certain critical radius are unstable to radial perturbations. The center-to-edge density contrast, mass, and radius of the marginally stable TES all increase with increasing average velocity dispersion. The FWHM of the column density profile is always smaller than the critical radius, by a larger factor at higher velocity dispersion, suggesting that observations need to probe beyond the FWHM to capture the full extent of turbulent cores. When applied to the highly turbulent regime typical of cluster-forming clumps, the critical mass and radius of the TES intriguingly resembles the typical mass and radius of observed star clusters.

Effects of Variable Mass, Disk-Like Structure, and Radiation Pressure on the Dynamics of Circular Restricted Three-Body Problem

In this paper, we intend to investigate the dynamics of the Circular Restricted Three-Body Problem. Here we assumed the primaries as the source of radiation and have variable mass. The gravitational perturbation from disk-like structure are also considered in this study. There exist five equilibrium points in this system. By considering the combined effect of disk–like structure and the mass transfer, we found that the classical collinear equilibrium points depart from the x–axis. We called these equilibrium points as quasi–collinear equilibrium points. Meanwhile, this combined effect also breaks the symmetry of triangular equilibrium point positions. We noted that the quasi–equilibrium points are unstable whereas the triangular equilibrium points are stable if the mass ratio μ is smaller than critical mass μc. Besides the mass ratio, the stability of triangular equilibrium points depend on time.

Optimal critical mass for the multi-species Keller-Segel model with rotational flux terms

Optimal critical mass for the multi-species Keller-Segel model with rotational flux terms

Radial blow-up in quasilinear Keller-Segel systems: approaching the full picture

Abstract The Neumann problem for the Keller-Segel system { u t = ∇ ⋅ ( D ( u ) ∇ u ) − ∇ ⋅ ( S ( u ) ∇ v ) , 0 = Δ v − μ + u , μ = − ∫ Ω u d x , is considered in n-dimensional balls Ω with n ⩾ 2 , with suitably regular and radially symmetric, radially nonincreasing initial data u 0. The functions D and S are only assumed to belong to C 2 ( [ 0 , ∞ ) ) and to satisfy D > 0 and S ⩾ 0 on [ 0 , ∞ ) as well as S ( 0 ) = 0 ; in particular, diffusivities with arbitrarily fast decay are included. In this general context, it is shown that it is merely the asymptotic behavior as ξ → ∞ of the expression I ( ξ ) := S ( ξ ) ξ 2 n D ( ξ ) , ξ > 0 , which decides about the occurrence of blow-up: Namely, it is seen that • if lim ξ → ∞ I ( ξ ) = 0 , then any such solution is global and bounded, that • if lim sup ξ → ∞ I ( ξ ) < ∞ and ∫ Ω u 0 is suitably small, then the corresponding solution is global and bounded, and that • if lim inf ξ → ∞ I ( ξ ) > 0 , then at each appropriately large mass level m, there exist radial initial data u 0 such that ∫ Ω u 0 = m , and that the associated solution blows up either in finite or in infinite time. This especially reveals the presence of critical mass phenomena whenever lim ξ → ∞ I ( ξ ) ∈ ( 0 , ∞ ) exists.

Ensuring that psychological interventions are delivered as intended on mental health inpatient wards.

Talk, Understand and Listen for InPatient Settings (TULIPS) was a multi-centred randomized control trial of an intervention that aimed to increase patient access to psychological therapies on acute mental health wards. This paper aims to: (i) describe a strategy for designing a psychological intervention that is implementable in inpatient mental health settings; (ii) describe methods for assessing the fidelity of interventions within these settings; (iii) report on the extent to which fidelity was achieved in the TULIPS trial. The TULIPS intervention was designed using information from a systematic review, stakeholder interviews, pilot work and a consensus workshop. We assessed fidelity to the model in terms of the delivery and dose of essential elements of the intervention, quality of intervention delivery, engagement of participants with the intervention and differentiation between the intervention and usual care. Although the TULIPS intervention targeted known barriers to the delivery of psychological interventions on mental health wards, we found issues in implementing aspects of the intervention that were dependent upon the participation of members of the multidisciplinary team. Psychologists were able to overcome barriers to delivering individual therapy to patients as this provision was not reliant on the availability of other staff. The intervention period in the study was 6 months. A greater period of time with a critical mass of psychological practitioners is needed to embed psychological interventions on inpatient wards. Our fidelity framework and assessment methods can be used by other researchers implementing and testing psychological therapies within inpatient environments.

Smoldering Ignition and Transition to Flaming Combustion of Pine Needle Fuel Beds: Effects of Bulk Density and Heat Supply

The smoldering of pine needle fuel beds (PNBs) has been a common subject of research because of its importance in initiating the rekindling of forest floor fires. Experimental studies of the coupling effects of the bulk density and external heat supply on smoldering in PNBs have been scarce up to now. In this study, laboratory smoldering experiments were conducted to study the coupling effects of bulk density (30–55 kg m−3) and heat supply (ignition-off temperature Toff = 190 °C and 230 °C). Different ignition modes were observed under the same conditions, including non- ignition (NI), flaming ignition (FI), and the smoldering-to-flaming (StF) transition. The results in this study showed that the bulk density had distinct effects on different ignition modes: the increase in the bulk density facilitated the StF transition but impeded the FI. The coupling effects between the bulk density and heat supply became more intricate, especially at lower bulk densities and at a reduced heat supply. Additionally, a simple energy balance equation was established to explain the coupling effects of bulk density and heat supply on ignition behavior. The critical mass loss rate (MLR) for the StF transition ranged from 0.01 g s−1 to 0.03 g s−1, while the critical MLR for FI was 0.035 g s−1. The modified combustion efficiency (MCE) index for the StF transition decreased from approximately 79.6% to 70.1% as the density increased from 30 kg m−3 to 55 kg m−3. In contrast, the MCE for FI was approximately 90% across all the bulk densities. The StF transition delay time increased from 50 s at 30 kg m−3 to 1296 s at 55 kg m−3 when Toff = 230 °C. Further reduction in heat supply led to an increase in the delay time for the StF transition by diminishing the intensity of smoldering combustion. This work advances the fundamental understanding of how heat supply and bulk density impact smoldering ignition modes, ultimately aiding in the development of wildfire prevention strategies.

Modeling and Simulations in Latin-American Generic Markets: Perspectives from Chilean Local Industry, Regulatory Agency, and Academia.

In the last 20 years, modeling and simulations (M&S) have gained increased attention in pharmaceutical sciences. International industry and world-reference agencies have used M&S to make cost-efficient decisions through the model-informed drug development (MIDD) framework. Modeling tools include biopredictive dissolution models, physiologically based pharmacokinetic models (PBPK), biopharmaceutic models (PBBM), and virtual bioequivalence, among many others. Regulatorily, health agencies are becoming more and more open to accept the use of M&S to support regulatory applications, including setting dissolution specifications, quality-by-design (QbD), postapproval changes (SUPAC), etc. Nonetheless, the potential of M&S has been only barely explored in Latin America (Latam) across different actors: industry, regulatory agencies, and even academia. In this manuscript, we discuss the challenges and opportunities for implementing M&S approaches in Latam. Perspectives of regional experts were shared in a workshop. Attendance (professionals from industry, regulator, academia, and clinicians) also shared their views via survey. The rational development of bioequivalent generics was considered the main opportunity for M&S in regional market, particularly the use of PBPK and PBBM. Nonetheless, a critical mass of modeling scientists is needed before Latin American industry and regulators can actually benefit from M&S. Collaborations (e.g., Academia-Industry and Academia-Regulatory) may be a path to develop applied research projects and train the future modelers. Reaching that critical mass, scientists from industry may apply modeling across generic drug development process and life cycle, while regulatory scientists may issue guidelines in local language to support regional industry. Only at that stage could the full potential of MIDD be reached in Latin American generic markets.

Flow-based nonperturbative simulation of first-order phase transitions

We present a flow-based method for simulating and calculating nucleation rates of first-order phase transitions in scalar field theory on a lattice. Motivated by recent advancements in machine learning tools, particularly normalizing flows for lattice field theory, we propose the “partitioning flow-based Markov chain Monte Carlo (PFMCMC) sampling” method to address two challenges encountered in normalizing flow applications for lattice field theory: the “mode-collapse” and “rare-event sampling” problems. Using a (2+1)-dimensional real scalar model as an example, we demonstrate the effectiveness of our PFMCMC method in modeling highly hierarchical order parameter probability distributions and simulating critical bubble configurations. These simulations are then used to facilitate the calculation of nucleation rates. We anticipate the application of this method to (3+1)-dimensional theories for studying realistic cosmological phase transitions.

The “Magic” Number: Women’s Critical Mass and Substantive Representation in Angola

The “Magic” Number: Women’s Critical Mass and Substantive Representation in Angola

Commentary: The Canadian Accounting Hall of Fame—An Analysis of Early Inductees and Immanent Critique*,†

ABSTRACTThe Canadian Accounting Hall of Fame (CAHF) has inducted 31 members during its first three years of operation, with the stated intent of establishing a critical mass of inductees “who have made significant contributions to the development of the Canadian accounting profession” and of creating “a curated biographical history of accounting in Canada.” This paper provides an analysis of the group and an immanent critique of CAHF given its mandate and aspirations. It begins with a close reading of CAHF's public statement of intent and policies to clarify what it is committed to achieving and to identify ambiguities and contradictions within its mandate. The characteristics of the initial inductees are then compared with baselines reflecting CAHF's mandate and are used to identify how ambiguities are resolved in practice. The current members of CAHF overrepresent financial reporting and auditing (compared with other areas of accounting competence), academics (compared with those in practice/industry), the more populated provinces (compared with the Prairies and Atlantic region), Chartered Accountants (compared with other legacy designations), and men (compared with women). Current practice also reveals unresolved ambiguities in the definitions of “Canada,” “Canadian,” “contribution,” and “impact,” as well as an underdeveloped presentation of historical context and documentation to interpret the inductees' contributions. Best practices for “retrospective cultural consecration institutions” are identified in the literature and align with CAHF procedures. The paper also examines critical commentary on CAHF in the press and identifies areas where its mandate is challenged by public expectations of inductees.

Climate board governance and carbon assurance – European evidence

Purpose This paper aims to investigate the effect of climate board governance based on (1) carbon change committees, (2) critical mass of female board members and (3) carbon-related executive compensation, on the voluntary implementation and quality of carbon assurance. Design/methodology/approach Using stakeholder and critical mass theories, 978 firm-year observations for European Union firms for the 2017–2021 period are collected. Climate board governance and carbon assurance proxies come from the Carbon Disclosure Project. Findings Correlation and logit regression analyses show that climate board governance significantly improves carbon assurance (quality). The findings are robust to various robustness and endogeneity checks and are of great importance for researchers, regulators and business practice. Originality/value This analysis mainly contributes to previous studies by using a combined sustainable board governance score as a major driver of corporate carbon assurance practices for the first time.

Software-Based automation of burnup calculations for the NUR research reactor using SCALE/TRITON T6-DEPL sequence

This work represents a key milestone in the development of a Monte Carlo Burnup Calculation System (MCBCS) specially tailored for the NUR research reactor. Developed using Python and leveraging the 3D Monte Carlo TRITON depletion sequence (T6-DEPL) within the SCALE code, MCBCS accurately simulates the reactor’s operating history. The paper provides an overview of MCBCS, focusing on its components, verification, and validation.The verification and validation process cover both fresh and burnt core conditions. For the fresh core, comparisons of excess reactivity, control rods worth, and critical configurations against experimental data and MCNP5 calculations showed good agreement. Burnup calculations were validated against measured core excess reactivity, reactivity worths of fuel assemblies, and neutron flux distribution. The system slightly underpredicted core excess reactivity by −2.95%, and discrepancies in reactivity worths remained within the 7% uncertainty range. Neutron flux distribution showed good consistency with minor location-specific deviations.Overall, these findings confirm MCBCS as a reliable and accurate tool for burnup calculations of the NUR research reactor.