bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Analysis of Blade-Casing Contacts in a Centrifugal Compressor: Vibration and Thermal Aspects
Authors: Guérin Nicolas , Gibert Claude , Thouverez Fabrice , Almeida Patricio
Published: January 2021

Due to an increasing need for efficiency of turbo-engines, rotor–stator clearances are being lowered. Therefore, new designs show higher probability for contacts between rotors and casings. When contacts occur, high dynamic excitation levels as well as high temperatures due to dissipative mechanical phenomena may be expected. While numerical investigations have been proposed in the past, experiments are of high interest to fully understand the underlying phenomena behind rotor–stator contact interactions. In order to assess this situation, and based on former work performed by part of the authors, a rotor–stator contact rig has been used to investigate the mechanical and thermal behavior of a centrifugal low-pressure helicopter engine compressor. This rig operates under vacuum conditions to significantly reduce influence of the air surrounding the studied components. A near-zero gap condition is set at rest, and then a rotational speed sweep allows to target the specific operating range of interest. Both structures are fitted with strain gauges (STGs), and a torquemeter is installed on the shaft to measure resistive phenomena on the bladed disk. A scanning laser Doppler vibrometer is aimed at the casing through a window to provide additional displacement measurements. Temperatures are measured by an array of thermocouples equally spaced around the casing, close to the expected contact area. Also, using temperature-sensitive markings, overall temperature mappings on the impeller are performed. During the tests, multiple contact phases have been identified through increased vibration and temperature levels, as well as torque and rotational speed variations. A comprehensive analysis of the dynamic and thermal phenomena occurring during these experimental tests is proposed in this paper. Dynamic measurements are analyzed in the time and frequency domains, and nodal diameter (ND) contents are evaluated as well through full spectrum analyses. As a result, major influences from synchronous excitations in the frequency range of interest but also of higher modal families are highlighted. Post-trial observations indicate severe contact conditions leading to very high temperatures, abradable coating removal, and material transfer between blade and casing.
Influence of Cardiorespiratory Fitness on Risk of Dementia and Dementia Mortality: A Systematic Review and Meta-Analysis of Prospective Cohort Studies
Authors: Lee Junga
Published: January 2021

The purpose of this meta-analysis was to investigate the influence of cardiorespiratory fitness (CF) levels on dementia risk and dementia mortality. MEDLINE and EMBASE databases were used to search for eligible studies from January 1990 to September 2019. To be included, the study was required to be a prospective cohort study that provided CF measurements and indicated relative risk and confidence intervals for the associations between CF and dementia risk and mortality. A total of six studies were selected for this meta-analysis. Low-level CF was associated with nearly three times greater risk of dementia (2.93, 95% confidence interval [1.31, 6.57]; p < .05) compared with a high-level CF. Enhanced CF levels decreased the risk of dementia, and an increase of one metabolic equivalent of task in the CF level reduced the risk of dementia and dementia mortality. Maintaining more than 12 metabolic equivalents of task of CF level was required to substantially decrease dementia risk and dementia mortality.
Heritable Gut Microbiome Associated with
Salmonella enterica
Serovar Pullorum Infection in Chickens
Authors: Ding Jinmei , Zhou Hao , Luo Lingxiao , Xiao Lu , Yang Kaixuan , Yang Lingyu , Zheng Yuming , Xu Ke , He Chuan , Han Chengxiao , Luo Huaixi , Qin Chao , Akinyemi Fisayo T. , Gu Caiju , Zhou Zhenxiang , Huang Qizhong , Meng He
Published: January 2021

The present study investigated the association among the host genome, the gut microbiome, and
S
. Pullorum infection in chickens. The results suggested that the gut microbial structure is altered in
S
. Pullorum-infected chickens.
The UK National Artificial Eye Questionnaire Study: comparisons between cosmetic shell and artificial eye users. Part 2: maintenance, management and quality of life
Authors: Ullrich Katja , Worrell Emma , Shapira Yinon , Litwin Andre , Malhotra Raman
Published: January 2021

Aims

To compare the unique experiences related to artificial eye (AE) versus cosmetic shell (CS) wear.

Methods

In this observational, cross-sectional study, the National Artificial Eye Questionnaire was employed nationwide within the National Health Service England. This second part of the study assesses daily management and care experiences, as well as visual function and quality of life aspects.

Results

Overall, 951 respondents wore an AE, while 238 wore a CS. Both AE and CS respondents rated a relatively high score for a beneficial effect of prosthesis polishing, with an average score of 80.08±0.87 versus 77.17±1.73 (p=0.13, respectively). CS respondents removed and cleaned their prosthesis more frequently than AE respondents (p<0.0001, p=0.002, respectively). CS respondents instilled lubrication more frequently than AE respondents (p=0.022) with 33.3% versus 43.7% of AE and CS wearers, respectively, lubricating on at least a daily basis. The overall QOL composite score was similar in both AE and CS groups (approximately 77%, p=0.74). Social functioning was similar, and relatively high in both groups (approximately 86%, p=0.77).

Conclusions

This study characterises unique aspects of CSs versus AEs in a large national cohort. The results should provide reinforcement to the gain in popularity of CSs.
Quantitative OCT angiography of the retinal microvasculature and choriocapillaris in highly myopic eyes with myopic macular degeneration
Authors: Zheng Feihui , Chua Jacqueline , Ke Mengyuan , Tan Bingyao , Yu Marco , Hu Qinglan , Cheung Chui Ming Gemmy , Ang Marcus , Lee Shu Yen , Wong Tien Yin ,   SNEC Retina Group, Schmetterer Leopold , Wong Chee Wai , Hoang Quan V
Published: January 2021

Purpose

To quantify retinal and choriocapillaris (CC) microvasculature in highly myopic (HM) eyes with myopic macular degeneration (MMD) using swept-source optical coherence tomography angiography (SS-OCTA).

Methods

162 HM eyes (spherical equivalent ≤ −6.0 dioptres or axial length (AL) ≥26.5 mm) from 98 participants were enrolled, including 60 eyes (37.0%) with tessellated fundus, 54 eyes (33.3%) with peripapillary diffuse chorioretinal atrophy (PDCA), 27 eyes (16.7%) with macular diffuse chorioretinal atrophy (MDCA) and 21 eyes (13.0%) with patchy or macular atrophy. PLEX Elite 9000 SS-OCTA was performed to obtain perfusion densities (PD) of the superficial and deep retinal capillary plexus, and CC signal voids (number, area and density).

Results

Retinal PD decreased with increasing severity of MMD. Multivariable analysis showed that after adjustment of age and other factors, retinal PD decreased significantly in eyes with longer AL (β≤−0.51, p<0.001) and with an MMD severity of MDCA or worse (β≤−1.63, p<0.001). Reduced retinal PD were significantly associated with worse vision (β≤−0.01, p≤0.04). In terms of CC signal voids, multivariable analysis showed that longer AL (p<0.001), but not MMD severity (p≥0.12) was significantly associated with CC signal void changes in the earliest stage of MMD.

Conclusion

We demonstrate significant OCTA alterations in the retina and CC in HM eyes with varying severities of MMD. In eyes with early-stage PDCA, lower retinal PD and more extensive CC signal voids are predominantly associated with increasing AL. In contrast, in eyes with MDCA or worse, MMD itself was associated with sparser retinal and CC circulation.
Choroidal macrovessels: multimodal imaging findings and review of the literature
Authors: Gallo Beatrice , de Silva Samantha R , Mahroo Omar A , Saihan Zubin , Patel Praveen J , Dowler Jonathan G , Pavesio Carlos , Keane Pearse A , Tufail Adnan , Sagoo Mandeep S
Published: January 2021

Background/aims

To describe clinical and multimodal imaging features in a cohort of choroidal macrovessels.

Methods

Demographics and multimodal imaging features of 16 eyes of 13 patients with choroidal macrovessels were reviewed. The multimodal imaging included colour fundus photography, fundus autofluorescence (FAF), spectral domain enhanced depth imaging optical coherence tomography (OCT), en face OCT, OCT-angiography (OCT-A), B-scan ultrasonography (US), fluorescein angiography (FFA) and indocyanine green angiography (ICGA).

Results

Three patients had bilateral involvement. On colour fundus photography, three patterns were evident (a clearly visible orange-red vessel; a track of pigmentary changes; spots of mild pigmentary changes). Vessel orientation was horizontal (11 eyes), oblique (4 eyes) or vertical (1 eye). In 2 eyes, the vessel was extra-macular. OCT in all cases showed a hyporeflective choroidal area with posterior shadowing and elevation of the overlying retina. Subretinal fluid was present in 4 eyes. FAF (12 eyes) was normal (7 eyes) or showed a hypofluorescent/hyperfluorescent track (4 eyes) or linear hyperautofluorescence (1 eye). En-face OCT (2 eyes) revealed the course of the macrovessel at the level of choroid and choriocapillaris. On OCT-A (2 eyes) the vessel had a reflectivity similar to surrounding vessels but larger diameter. B-scan US (8 eyes) showed a nodular hypoechogenic lesion. FFA (5 eyes) showed early focal hyperfluorescence (4 eyes) not increasing in later phases, or was normal (1 eye). ICGA (6 eyes) showed early hyperfluorescence of the vessel.

Conclusions

Choroidal macrovessels can mimic other entities, leading to underdiagnosis. Appreciating relevant features on different imaging modalities will aid a correct diagnosis.
Health-promoting behaviours and concussion history are associated with cognitive function, mood-related symptoms and emotional–behavioural dyscontrol in former NFL players: an NFL-LONG Study
Authors: Walton Samuel R , Kerr Zachary Y , Brett Benjamin L , Chandran Avinash , DeFreese J D , Smith-Ryan Abbie E , Stoner Lee , Echemendia Ruben J , McCrea Michael , Meehan, III William P , Guskiewicz Kevin M
Published: January 2021

Objectives

To examine the relationships among self-reported sport-related concussion (SRC) history and current health-promoting behaviours (exercise frequency, diet quality and sleep duration) with self-reported measures of brain health (cognitive function, symptoms of depression and anxiety and emotional–behavioural dyscontrol) in former NFL players.

Methods

In this cross-sectional study, a questionnaire was sent to former NFL players. Respondents reported SRC history (categorical: 0; 1–2; 3–5; 6–9; 10+ concussions), number of moderate-to-vigorous aerobic and resistance exercise sessions per week, diet quality (Rapid Eating Assessment for Participants—Shortened) and average nightly sleep duration. Outcomes were Patient-Reported Outcomes Measurement Information System Cognitive Function, Depression, and Anxiety, and Neuro-QoL Emotional-Behavioral Dyscontrol domain T-scores. Multivariable linear regression models were fit for each outcome with SRC history, exercise frequency, diet quality and sleep duration as explanatory variables alongside select covariates.

Results

Multivariable regression models (n=1784) explained approximately 33%–38% of the variance in each outcome. For all outcomes, SRC history (0.144≤|β|≤0.217) was associated with poorer functioning, while exercise frequency (0.064≤|β|≤0.088) and diet quality (0.057≤|β|≤0.086) were associated with better functioning. Sleeping under 6 hours per night (0.061≤|β|≤0.093) was associated with worse depressive symptoms, anxiety and emotional–behavioural dyscontrol.

Conclusion

Several variables appear to be associated with mood and perceived cognitive function in former NFL players. SRC history is non-modifiable in former athletes; however, the effects of increasing postplaying career exercise frequency, making dietary improvements, and obtaining adequate sleep represent important potential opportunities for preventative and therapeutic interventions.
Geographical clustering and socioeconomic factors associated with hypoglycemic events requiring emergency assistance in Andalusia (Spain)
Authors: Gomez-Peralta Fernando , Abreu Cristina , Benito Manuel , Barranco Rafael J
Published: January 2021

Introduction

The geographical distribution of hypoglycemic events requiring emergency assistance was explored in Andalusia (Spain), and potentially associated societal factors were determined.

Research design and methods

This was a database analysis of hypoglycemia requiring prehospital emergency assistance from the Public Company for Health Emergencies (Empresa Pública de Emergencias Sanitarias (EPES)) in Andalusia during 2012, which served 8 393 159 people. Databases of the National Statistics Institute, Basic Spatial Data of Andalusia and System of Multiterritorial Information of Andalusia were used to retrieve spatial data and population characteristics. Geographic Information System software (QGIS and GeoDA) was used for analysis and linkage across databases. Spatial analyses of geographical location influence in hypoglycemic events were assessed using Moran’s I statistics, and linear regressions were used to determine their association with population characteristics.

Results

The EPES attended 1 137 738 calls requesting medical assistance, with a mean hypoglycemia incidence of 95.0±61.6 cases per 100 000 inhabitants. There were significant differences in hypoglycemia incidence between basic healthcare zones attributable to their geographical location in the overall population (Moran’s I index 0.122, z-score 7.870, p=0.001), women (Moran’s I index 0.088, z-score 6.285, p=0.001), men (Moran’s I index 0.076, z-score 4.914, p=0.001) and aged >64 years (Moran’s I index 0.147, z-score 9.753, p=0.001). Hypoglycemia incidence was higher within unemployed individuals (β=0.003, p=0.001) and unemployed women (β=0.005, p=0.001), while lower within individuals aged <16 years (β=−0.004, p=0.040), higher academic level (secondary studies) (β=−0.003, p=0.004) and women with secondary studies (β=−0.005, p<0.001). In subjects aged >64 years, lower rate of hypoglycemia was associated with more single-person homes (β=−0.008, p=0.022) and sports facilities (β=−0.342, p=0.012).

Conclusions

This analysis supports the geographical distribution of hypoglycemia in the overall population, both genders and subjects aged >64 years, which was affected by societal factors such as unemployment, literacy/education, housing and sports facilities. These data can be useful to design specific prevention programs.
Trends in player body mass at men’s and women’s Rugby World Cups: a plateau in body mass and differences in emerging rugby nations
Authors: Tucker Ross , Lancaster Stuart , Davies Phil , Street Gary , Starling Lindsay , de Coning Cian , Brown James
Published: January 2021

Objectives

This study assessed the mass of international rugby players in the men’s and women’s Rugby World Cups between 1991 and 2019. The objective was to quantify changes in mass of players by position, and to compare changes between men and women, and between established (Tier 1 (T1)) and emerging (Tier 2 (T2)) rugby nations.

Setting

Rugby World Cups from 1991 to 2019 for men’s players and 2010 to 2017 for women’s players.

Participants

4447 elite male and 958 elite female players.

Primary and secondary outcome measures

Player body mass, grouped as men and women, T1 and T2 nations, and by playing position, assessed over time.

Results

Men’s player mass increased significantly between 1991 and 2019 (T1 overall 9.7% increase), but this increase occurred almost entirely up to 2011. Women’s forwards mass increased by 4.8% in T1, with no changes in T2 or backs from either tier. Significant differences in mass were found between T1 and T2 forwards and backs for both men and women.

Conclusions

The body mass of men’s players has stabilised after initial increases following professionalisation. Player body mass may be approaching a plateau, beyond which no further performance advantages occur. Changes to laws and tactical approaches by coaches may have contributed to this, by changing match demands on players, necessitating endurance, agility and speed. Trends in the evolution of T2 players suggest a barrier to identifying and developing heavy athletic players, and may require intervention to ensure competitive parity.
Can police shootings be reduced by requiring officers to document when they point firearms at citizens?
Authors: Shjarback John A , White Michael D , Bishopp Stephen A
Published: January 2021

Objective

To examine the impact of a novel firearm ‘pointing’ policy that requires officers to document when they directly point their guns at citizens.

Methods

Sixteen years (2003–2018) of narrative officer-involved shooting (OIS) reports from the Dallas Police Department were qualitatively coded to explore both the total frequency and specific characteristics of OIS before and after the policy change in 2013.

Results

χ2tests found that the firearm pointing policy was associated with a reduction in the proportion of ‘threat perception failure’ shootings (ie, those where an officer mistakes an item for a gun). Auto Regressive Integrated Moving Average analysis found that the policy change was associated with a gradual, permanent reduction in total OIS; however, that impact was not immediate.

Conclusions

Firearm pointing policies have the potential to alter organisational behaviour, particularly in highly discretionary shootings. It is unclear whether the specific mechanisms for the changes include more accountability through constrained discretion, reduced options to handle situations once officers’ guns are drawn and pointed, or an effect on officers’ timing and vision during ambiguous scenarios.

Policy implications

Although organisational change may be a long and complex process, reductions in OIS can prevent serious injuries and death. The policy change did not lead to an increase in the proportion of officers injured during OIS incidents.
Comprehensive evaluation of BRCA1/2 variant interpretation ability among laboratories in China
Authors: Shao Kang , Wang Ruixia , Qu Shoufang , Zhang Wenxin , Yu Ting , Cao Boyang , Dai Pingping , Zhu Anna , Zhang Jianguang , Wang Juan , Wang Lusheng , Zhu Shida , Wu Kui , Yang Xuexi , Chang Xiaoyan , Chen Fang , Huang Jie
Published: January 2021

High-quality interpretation of BRCA1/2 variants plays a critical role in the clinical practice of precision medicine. However, a comprehensive system to evaluate the quality and accuracy of variant interpretation has yet to be established. This study investigates the performance of an interpretation system in evaluating the capacities of BRCA1/2 interpretation among distinct laboratories in China. The evaluation system is based on a reference database that contains 750 different variants in BRCA1/2. Evaluation was performed among 41 laboratories in China. We classified their performance into five levels. Only level A was considered qualified. This level allows for a 0.3% error rate for clinical decision-related misinterpretation; 26 of 41 laboratories (63%) met the qualified standard, while 7 laboratories were at levels D and E, which indicated egregious mistakes and systemic problems in variant interpretation. Due to strict quality demands, the interpretation of several variants was amended, which largely influenced the quality rate. The number of qualified laboratories would decrease from 26 to 17 if those incorrect recommended interpretations were not corrected. This evaluation system provides a potential approach for standardisation of variant interpretation and lowers the discordance of variant interpretation between different laboratories. A well-designed interpretation ability evaluation is essential to evaluate the interpretation level of laboratories before they provide service in real-world clinical settings.
Evaluating benthic impact of the Gulf of Maine lobster fishery using the Swept Area Seabed Impact (SASI) model
Authors: Goode Andrew G. , Grabowski Jonathan H. , Brady Damian C.
Published: January 2021

The Magnuson–Stevens Fishery Conservation and Management Act mandates US fisheries minimize adverse effects of fishing on essential fish habitat (EFH). The Gulf of Maine (GoM) American lobster (Homarus americanus) fishery is the most valuable US fishery and can deploy more than three million traps annually. To date, the impact of this fishery on benthic EFH has not been addressed quantitatively. To evaluate the impact of the GoM lobster fishery on EFH, we incorporated lobster fishing effort into a model linking habitat susceptibility and recovery to area impacted by fishing gear: the Swept Area Seabed Impact model. Impact to EFH was localized along the coast and highest along midcoast Maine. Upwards of 13% of the benthos is in the process of recovery, but between 99.92% and 99.96% of initially affected habitat fully recovers. These estimates suggest that lobster fishing negligibly contributes to accumulation of EFH damage in the GoM due to the expansive area fished and the small footprint of each trap. Identifying areas of persistent impact is crucial in developing effective fisheries management for critical marine habitats.
Natural recovery of skid trails: a review
Authors: DeArmond Daniel , Ferraz João B.S. , Higuchi Niro
Published: January 2021

In recent years, the study of skid trail recovery processes has gained momentum. In this review, 121 studies on various aspects of skid trail recovery were evaluated to determine when, where, and how the dominant factors that influence the process of recuperation occur. These studies were located proportionally in the following forest biomes: temperate (60%), tropical (31%), and boreal (9%). Research focused mainly on soil physical properties to ascertain if there had been evidence of recovery. The majority of studies of a decade or less after abandonment demonstrated that heavily used skid trails had not recovered. On the contrary, lightly used skid trails did present full recoveries over the same time span. Soil recovery tended to occur in medium- to coarse-textured soils in temperate and boreal forests. Considering all forest biomes, the impacts of compaction persisted at least two to five decades after logging operations. The impacts were evident in diminished tree heights and volumes from trees growing on skid trails. The last 50 years of research indicates that skid trails, globally, do recover from compaction, albeit slowly.
Maximizing the Net Present Value in Project Scheduling Under Periodic Inflation
Authors: Peymankar Mahboobe , Ranjbar Mohammad
Published: January 2021

We investigate a project scheduling problem in which cash flows are periodically variable, and we aim to maximize the net present value (NPV). For each activity, a set of cash flows is considered where each one pertains to a particular period. This setting is compatible with inflation rates that may well occur in some countries with unstable economic situations where the occurrence times of inflation are sometimes known in advance. In this case, the project can be scheduled more suitably to abate probable pitfalls. In this paper, we investigate the problem in two settings: deterministic and stochastic cash flows. In the deterministic case, in each period we consider the expected value of cash flows of each activity as a constant and develop an integer linear programming model in conjunction with a branch-and-bound algorithm to solve the problem optimally. Moreover, we develop a multi-stage stochastic programming (MSSP) model to formulate the stochastic version of the problem. Using a set of randomly generated test instances and extensive computational results, we analyze the performance of our developed solution approaches. In addition, we compare the deterministic and stochastic models and analyze the sensitivity of the most important parameters.
The Coordinator Role of Trade Credit Contract for Coordinating Integrated Pricing and Periodic Review Inventory Decisions With Stochastic Demand
Authors: Johari Maryam , Hosseini-Motlagh Seyyed-Mahdi , Nematollahi Mohammadreza
Published: January 2021

The purpose of this study is to analytically coordinate joint pricing and periodic review ordering choices for a supply chain (SC) facing stochastic price-dependent demand. In this paper, first, the optimal inventory and pricing strategies made by SC members are obtained under decentralized and centralized models. Thereafter, employing a trade credit contract, it proposes to provide a win–win coordination for the investigated SC. Sensitivity analyses are provided both analytically and numerically which indicate the significance of trade credit contracts in improving both customer service level and customer satisfaction. The results indicate that using trade credit contracts, the coordination of joint pricing and periodic review ordering choices is achievable. Moreover, the proposed trade credit contract has a unique feature in achieving more economic benefit compared to the centralized model under some circumstances. In addition, sensitivity analyses reveal that the coordination of integrated periodic review ordering and pricing choices is beneficial, especially for items with high price sensitivity and high demand uncertainty. Our findings also show the applicability of the trade credit contract for an SC facing highly uncertain demand.
Applying a New Multi-Dimensional Archimedean Copula on Step Stress Accelerated Life Testing with Competing Risks
Authors: Abdel Ghaly A. A. , Aly H. M. , Salah R. N.
Published: January 2021

A copula approach decomposes the joint distribution of random variables into marginal distributions of individual variables and the copula form that links the marginals together. When a researcher is dealing with a modeling problem, he is confronted with obtaining the best possible fit for the observed dependence structure. One possibility is to construct a new ideal copula that can describe the observed dependence. Finding a flexible multi-dimensional copula for modeling dependence is still quite challenging. In this paper, we will construct a new multi-dimensional Archimedean copula function that is characterized by a generator with two parameters which allows for more flexibility in modeling dependence. Moreover, we will apply the new constructed copula on step stress accelerated life testing with dependent competing risks under type II censoring. The point estimates of the unknown parameters are obtained using the maximum likelihood method. Also, the approximate and the parametric bootstrap confidence intervals are constructed. Numerical analysis including simulated data and a real life data about aerospace electrical connector is conducted to study the performance of our proposed copula function.
Yetter–Drinfeld category for the quasi-Turaev group coalgebra and cocycle deformation
Authors: Lu Daowei , Ning Yan
Published: January 2021

Let [Formula: see text] be a group and [Formula: see text] a quasi-Turaev group coalgebra over [Formula: see text]. In this paper, we firstly construct the category [Formula: see text] of left-right Yetter–Drinfeld modules over [Formula: see text], generalizing both of the Yetter–Drinfeld modules over Hopf group coalgebra and quasi-Hopf algebra, and prove that this category is isomorphic to the center of the representation category of [Formula: see text]. Next, we prove that the full subcategory [Formula: see text] consisting of all finite dimensional Yetter–Drinfeld modules over [Formula: see text] is autonomous. Finally, when [Formula: see text] is reduced to a Turaev group coalgebra, we introduce the dual 2-cocycle [Formula: see text] of [Formula: see text], and dual cocycle deformation [Formula: see text], and show that [Formula: see text] is isomorphic to [Formula: see text] as braided monoidal category.
THE LONG-TERM CHANGES OF EMISSION DRIVING FORCES IN EUROPEAN POWER AND HEAT SECTOR AND THEIR IMPACT ON THE DECARBONIZATION PATHWAYS IN EU ENERGY SECTOR SINCE 1990
Authors: NIEMIERKA ELŻBIETA , JADWISZCZAK PIOTR
Published: January 2021

The Public Electricity and Heat Production (PEHP) is the most emissive sector in European economy. The characteristic features of PEHP contribute to the importance of its mitigation role. In this study, the decarbonization potential of energy sector was retrospectively analyzed. Proposed algorithm contained, at the first layer, the year-by-year data analysis and calculation while at the second graphical interpretation and pattern grouping. Despite the double-layering, the developed approach included the three following stepwise stages: the CO2 emission alternatives scenarios pathways methodology, the CO2 emission driving forces modes and influence weight methodology, and the transformation pattern identifying and grouping. Based on 1990–2017 CO2 emission inventories, the investigation of long-term PEHP decarbonization in 26 European countries was performed, in year-by-year and country-by-country processing. All results and findings have become the foundation for describing achieved decarbonization goals and 27 years mitigation ways. The Energy Consumption (EC) and Emission Factor (EF) have been pointed as a key driving forces of CO2 emission and as a key development indicator of PEHP sectoral transformation structure. Based on the developed country-by-country graphical interpretation interface, the five key patterns of PEHP decarbonization processes in European countries were observed and defined. The algorithm which has been applied and tested in 26 countries for 27 years was proved to be a universal and flexible tool to determine the lack of a utilitarian path of PEHP CO2 emission mitigation in Europe.
AAAI/ACM SIGAI job fair 2020
Authors: Albert Michael , Dickerson John P
Published: January 2021

For the sixth year running, AAAI and ACM SIGAI jointly ran the popular AAAI/ACM SIGAI Job Fair. In lockstep with the growth of AAAI and the growth of the greater artificial intelligence and machine learning (AI/ML) community, our once-small job fair also grew. This year, thirty-eight companies and universities formally attended---typically with a booth, team of recruiters, swag, and other representatives---increasing from twenty-six companies during the job fair's previous run in 2019, and twenty-one companies in the year prior to that. Last year, we purchased a dedicated domain---https://aaaijobfair.com/---for the job fair. This year, we provided a link on that site through which job-seekers---students, postdocs, practitioners, and maybe even a few faculty---could upload their resumes or CVs. We then shared that data and contact information for slightly under four hundred job-seekers with participants on the other side: prospective employers.
Taming the State-space Explosion in the Makespan Optimization of Flexible Manufacturing Systems
Authors: Bastos João , Voeten Jeroen , Stuijk Sander , Schiffelers Ramon , Corporaal Henk
Published: January 2021

This article presents a modular automaton-based framework to specify flexible manufacturing systems and to optimize the makespan of product batches. The Batch Makespan Optimization (BMO) problem is NP-Hard and optimization can therefore take prohibitively long, depending on the size of the state-space induced by the specification. To tame the state-space explosion problem, we develop an algebra based on automata equivalence and inclusion relations that consider both behavior and structure. The algebra allows us to systematically relate the languages induced by the automata, their state-space sizes, and their solutions to the BMO problem. Further, we introduce a novel constraint-based approach to systematically prune the state-space based on the the notions of nonpermutation-repulsiveness and permutation-attractiveness. We prove that constraining a nonpermutation-repulsing automaton with a permutation-attracting constraint always reduces the state-space. This approach allows us to (i) compute optimal solutions of the BMO problem when the (additional) constraints are taken into account and (ii) compute bounds for the (original) BMO problem (without using the constraints). We demonstrate the effectiveness of our approach by optimizing an industrial wafer handling controller.
Events
Authors: Dennis Louise A.
Published: January 2021

This section features information about upcoming events relevant to the readers of AI Matters, including those supported by SIGAI. We would love to hear from you if you are are organizing an event and would be interested in cooperating with SIGAI. For more information about conference support visit sigai.acm.org/activities/requesting sponsorship.html.
AI education matters
Authors: Neller Todd W.
Published: January 2021

In this column, we recount the history of EAAI mentored undergraduate research challenges from 2014 through the present and share a vision of how such offerings may become more diverse and engage a broader range of faculty mentors and undergraduate researchers.

Unlike many academic disciplines, Computer Science undergraduate majors currently are not usually required to take or even offered a research methods course. Even so, many graduate schools desire to admit graduate students with undergraduate research experience. The EAAI Symposium has historically affirmed the value of mentored undergraduate research as an important part of undergraduate AI education. It has expressed this value through the support of a number of mentored undergraduate research challenges, described below.
AI policy matters
Authors: Medsker Larry
Published: January 2021

AI Policy Matters is a regular column in
AI Matters
featuring summaries and commentary based on postings that appear twice a month in the
AI Matters
blog (https://sigai.acm.org/aimatters/blog/). We welcome everyone to make blog comments so we can develop a rich knowledge base of information and ideas representing the SIGAI members.
A computational interpretation of compact closed categories: reversible programming with negative and fractional types
Authors: Chen Chao-Hong , Sabry Amr
Published: January 2021

Compact closed categories include objects representing higher-order functions and are well-established as models of linear logic, concurrency, and quantum computing. We show that it is possible to construct such compact closed categories for conventional sum and product types by defining a dual to sum types, a negative type, and a dual to product types, a fractional type. Inspired by the categorical semantics, we define a sound operational semantics for negative and fractional types in which a negative type represents a computational effect that ``reverses execution flow'' and a fractional type represents a computational effect that ``garbage collects'' particular values or throws exceptions.

Specifically, we extend a first-order reversible language of type isomorphisms with negative and fractional types, specify an operational semantics for each extension, and prove that each extension forms a compact closed category. We furthermore show that both operational semantics can be merged using the standard combination of backtracking and exceptions resulting in a smooth interoperability of negative and fractional types. We illustrate the expressiveness of this combination by writing a reversible SAT solver that uses backtracking search along freshly allocated and de-allocated locations. The operational semantics, most of its meta-theoretic properties, and all examples are formalized in a supplementary Agda package.
Learning the boundary of inductive invariants
Authors: Feldman Yotam M. Y. , Sagiv Mooly , Shoham Sharon , Wilcox James R.
Published: January 2021

We study the complexity of invariant inference and its connections to exact concept learning. We define a condition on invariants and their geometry, called the fence condition, which permits applying theoretical results from exact concept learning to answer open problems in invariant inference theory. The condition requires the invariant's boundary---the states whose Hamming distance from the invariant is one---to be backwards reachable from the bad states in a small number of steps. Using this condition, we obtain the first polynomial complexity result for an interpolation-based invariant inference algorithm, efficiently inferring monotone DNF invariants with access to a SAT solver as an oracle. We further harness Bshouty's seminal result in concept learning to efficiently infer invariants of a larger syntactic class of invariants beyond monotone DNF. Lastly, we consider the robustness of inference under program transformations. We show that some simple transformations preserve the fence condition, and that it is sensitive to more complex transformations.
Verifying correct usage of context-free API protocols
Authors: Ferles Kostas , Stephens Jon , Dillig Isil
Published: January 2021

Several real-world libraries (e.g., reentrant locks, GUI frameworks, serialization libraries) require their clients to use the provided API in a manner that conforms to a context-free specification. Motivated by this observation, this paper describes a new technique for verifying the correct usage of context-free API protocols. The key idea underlying our technique is to over-approximate the program’s feasible API call sequences using a context-free grammar (CFG) and then check language inclusion between this grammar and the specification. However, since this inclusion check may fail due to imprecision in the program’s CFG abstraction, we propose a novel refinement technique to progressively improve the CFG. In particular, our method obtains counterexamples from CFG inclusion queries and uses them to introduce new non-terminals and productions to the grammar while still over-approximating the program’s relevant behavior.

We have implemented the proposed algorithm in a tool called CFPChecker and evaluate it on 10 popular Java applications that use at least one API with a context-free specification. Our evaluation shows that CFPChecker is able to verify correct usage of the API in clients that use it correctly and produces counterexamples for those that do not. We also compare our method against three relevant baselines and demonstrate that CFPChecker enables verification of safety properties that are beyond the reach of existing tools.
Semantics-guided synthesis
Authors: Kim Jinwoo , Hu Qinheping , D'Antoni Loris , Reps Thomas
Published: January 2021

This paper develops a new framework for program synthesis, called semantics-guided synthesis (SemGuS), that allows a user to provide both the syntax and the semantics for the constructs in the language. SemGuS accepts a recursively defined big-step semantics, which allows it, for example, to be used to specify and solve synthesis problems over an imperative programming language that may contain loops with unbounded behavior. The customizable nature of SemGuS also allows synthesis problems to be defined over a non-standard semantics, such as an abstract semantics. In addition to the SemGuS framework, we develop an algorithm for solving SemGuS problems that is capable of both synthesizing programs and proving unrealizability, by encoding a SemGuS problem as a proof search over Constrained Horn Clauses: in particular, our approach is the first that we are aware of that can prove unrealizabilty for synthesis problems that involve imperative programs with unbounded loops, over an infinite syntactic search space. We implemented the technique in a tool called MESSY, and applied it to SyGuS problems (i.e., over expressions), synthesis problems over an imperative programming language, and synthesis problems over regular expressions.
Optimal prediction of synchronization-preserving races
Authors: Mathur Umang , Pavlogiannis Andreas , Viswanathan Mahesh
Published: January 2021

Concurrent programs are notoriously hard to write correctly, as scheduling nondeterminism introduces subtle errors that are both hard to detect and to reproduce. The most common concurrency errors are (data) races, which occur when memory-conflicting actions are executed concurrently. Consequently, considerable effort has been made towards developing efficient techniques for race detection. The most common approach is dynamic race prediction: given an observed, race-free trace σ of a concurrent program, the task is to decide whether events of σ can be correctly reordered to a trace σ
*
that witnesses a race hidden in σ.

In this work we introduce the notion of sync(hronization)-preserving races. A sync-preserving race occurs in σ when there is a witness σ
*
in which synchronization operations (e.g., acquisition and release of locks) appear in the same order as in σ. This is a broad definition that strictly subsumes the famous notion of happens-before races. Our main results are as follows. First, we develop a sound and complete algorithm for predicting sync-preserving races. For moderate values of parameters like the number of threads, the algorithm runs in Õ(
N
) time and space, where
N
is the length of the trace σ. Second, we show that the problem has a Ω(
N
/log
2
N
) space lower bound, and thus our algorithm is essentially time and space optimal. Third, we show that predicting races with even just a single reversal of two sync operations is NP-complete and even W1-hard when parameterized by the number of threads. Thus, sync-preservation characterizes exactly the tractability boundary of race prediction, and our algorithm is nearly optimal for the tractable side. Our experiments show that our algorithm is fast in practice, while sync-preservation characterizes races often missed by state-of-the-art methods.
Relatively complete verification of probabilistic programs: an expressive language for expectation-based reasoning
Authors: Batz Kevin , Kaminski Benjamin Lucien , Katoen Joost-Pieter , Matheja Christoph
Published: January 2021

We study
a syntax for specifying quantitative
assertions
—functions mapping program states to numbers—for probabilistic program verification. We prove that our syntax is expressive in the following sense: Given any probabilistic program
C
, if a function
f
is expressible in our syntax, then the function mapping each initial state σ to the expected value of evaluated in the final states reached after termination of
C
on σ (also called the weakest preexpectation wp[
C
](
f
)) is also expressible in our syntax.

As a consequence, we obtain a
relatively complete verification system
for reasoning about expected values and probabilities in the sense of Cook: Apart from proving a single inequality between two functions given by syntactic expressions in our language, given
f
,
g
, and
C
, we can check whether
g
≼ wp[
C
](
f
).
Combining the top-down propagation and bottom-up enumeration for inductive program synthesis
Authors: Lee Woosuk
Published: January 2021

We present an effective method for scalable and general-purpose inductive program synthesis. There have been two main approaches for inductive synthesis: enumerative search, which repeatedly enumerates possible candidate programs, and the top-down propagation (TDP), which recursively decomposes a given large synthesis problem into smaller subproblems. Enumerative search is generally applicable but limited in scalability, and the TDP is efficient but only works for special grammars or applications. In this paper, we synergistically combine the two approaches. We generate small program subexpressions via enumerative search and put them together into the desired program by using the TDP. Enumerative search enables to bring the power of TDP into arbitrary grammars, and the TDP helps to overcome the limited scalability of enumerative search. We apply our approach to a standard formulation, syntax-guided synthesis (SyGuS), thereby supporting a broad class of inductive synthesis problems. We have implemented our approach in a tool called Duet and evaluate it on SyGuS benchmark problems from various domains. We show that Duet achieves significant performance gains over existing general-purpose as well as domain-specific synthesizers.
The taming of the rew: a type theory with computational assumptions
Authors: Cockx Jesper , Tabareau Nicolas , Winterhalter Théo
Published: January 2021

Dependently typed programming languages and proof assistants such as Agda and Coq rely on computation to automatically simplify expressions during type checking. To overcome the lack of certain programming primitives or logical principles in those systems, it is common to appeal to axioms to postulate their existence. However, one can only postulate the bare existence of an axiom, not its computational behaviour. Instead, users are forced to postulate equality proofs and appeal to them explicitly to simplify expressions, making axioms dramatically more complicated to work with than built-in primitives. On the other hand, the equality reflection rule from extensional type theory solves these problems by collapsing computation and equality, at the cost of having no practical type checking algorithm. This paper introduces Rewriting Type Theory (RTT), a type theory where it is possible to add computational assumptions in the form of rewrite rules. Rewrite rules go beyond the computational capabilities of intensional type theory, but in contrast to extensional type theory, they are applied automatically so type checking does not require input from the user. To ensure type soundness of RTT—as well as effective type checking—we provide a framework where confluence of user-defined rewrite rules can be checked modularly and automatically, and where adding new rewrite rules is guaranteed to preserve subject reduction. The properties of RTT have been formally verified using the MetaCoq framework and an implementation of rewrite rules is already available in the Agda proof assistant.
KOH Based Method for the Determination of Oxygen Content in Ball Milled SiOx Material
Authors: Dressler R. A. , Dahn J. R.
Published: January 2021

SiOx is a silicon-based anode material for Li-ion batteries that has a high specific capacity and good cycle life. Lithiation of SiOx results in the formation of active Si cores surrounded by an inactive stabilizing matrix of irreversible lithium silicates and lithium oxides. SiOx with adjustable values of x can be synthesized by roller milling under oxygen flow, with the oxygen content being controlled by the amount of time spent milling in oxygen vs milling under argon. A fast and inexpensive oxygen content determination method was needed for determination of the oxygen content in SiOx as the roller milling process proceeded. A simple 4-step procedure to determine the oxygen content in SiOx is presented using a KOH solution, aluminized pouch bags, and Archimedes gas quantification measurements. This method can serve as a quick and inexpensive substitute to traditional oxygen content determination measurements such as gas fusion analysis.