Numerically-aware orderings for sparse symmetric indefinite linear systems

Sparse symmetric indefinite problems arise in a large number of important application areas; they are often solved through the use of an LDLT factorization via a sparse direct solver. Whilst for many problems, prescaling the system matrix A is sufficient to maintain stability of the factorization, for a small but important fraction of problems numerical pivoting is required. Pivoting often incurs a significant overhead and consequently a number of techniques have been proposed to try and limit the need for pivoting. In particular, numerically-aware ordering algorithms may be used, that is, orderings that depend not only on the sparsity pattern of A but also on the values of its (scaled) entries. Current approaches identify large entries of A and symmetrically permute them onto the subdiagonal where they can be used as part of a 2x2 pivot. This is numerically effective, but the fill in the factor L and hence the runtime of the factorization and subsequent triangular solves may be significantly increased over a standard ordering if no pivoting is required. We present a new algorithm that combines a matching-based approach with a numerically-aware nested dissection ordering. Numerical comparisons with current approaches for some tough symmetric indefinite problems are given

A max-plus approach to incomplete Cholesky factorization preconditioners

We present a new method for constructing incomplete Cholesky factorization preconditioners for use in solving large sparse symmetric positive-definite linear systems. This method uses max-plus algebra to predict the positions of the largest entries in the Cholesky factor and then uses these positions as the sparsity pattern for the preconditioner. Our method builds on the max-plus incomplete LU factorization preconditioner recently proposed in [J. Hook and F. Tisseur, Incomplete LU preconditioner based on max-plus approximation of LU factorization, MIMS Eprint 2016.47, Manchester, 2016] but applied to symmetric positive-definite matrices, which comprise an important special case for the method and its application. An attractive feature of our approach is that the sparsity pattern of each column of the preconditioner can be computed in parallel. Numerical comparisons are made with other incomplete Cholesky factorization preconditioners using problems from a range of practical applications. We demonstrate that the new preconditioner can outperform traditional level-based preconditioners and offer a parallel alternative to a serial limited-memory based approach

The influence of femoral structure, hip capsular constraints, and gluteal muscle strength and activation on temporal patterns of functional valgus collapse

Functional valgus collapse (a combination of knee abduction and internal rotation and hip adduction and internal rotation) is a modifiable lower extremity movement pattern commonly associated with anterior cruciate ligament (ACL) injuries in females. Though the gluteus maximus and gluteus medius have frequently been named contributors to functional valgus collapse, evidence supporting their role in lower extremity movement has been inconsistent, and could in part be due to methodological differences between studies and the accepted practice of analyzing discrete variables instead of overall movement patterns. Better elucidation of gluteal muscle influence on lower extremity biomechanics may be a critical step for the reduction of ACL injury rates, as neuromuscular dysfunction is likely more responsive to injury prevention efforts than are other risk factors such as bony anatomy, ligament quality, or hormonal influences, that are more difficult to modify. Therefore, the purpose of this study was to 1) describe the neuromechanical profiles throughout the landing phase of single-leg and double-leg forward landings in males and females, 2) quantify the contributions of gluteal muscle strength and activation to peak angles and moments of functional valgus collapse after controlling for one’s femoral alignment, and 3) explore the association between gluteal muscle function and overall functional valgus collapse throughout the landing phase. To accomplish this, 45 females and 45 males with no history of knee surgery were measured for femoral anteversion, hip ROM, and hip strength and then underwent biomechanical testing during single-leg and double-leg forward landings to examine muscle activation and 3-dimensional biomechanics. Data were analyzed using conventional group and correlative analyses and also with statistical parametric mapping (SPM), which allowed for a more comprehensive examination of the entire biomechanical time series. Biomechanical variables of interest included joint angles and moments comprising functional valgus collapse: hip adduction and internal rotation and knee abduction and internal rotation. In the comparison between single-leg and double-leg landings by sex, sex differences in the frontal plane were task dependent, though females maintained greater absolute knee abduction and hip adduction throughout the landing phases. Sex by task interactions revealed that females landed with smaller knee adduction angles than males, particularly during the single-leg landing (p=.03), while females’ knee abduction excursion was greater than males’, particularly during the double-leg landing (p=.01). Across task, females displayed 4.1° greater peak knee abduction than males (p=.002), and this was specific to 37-46% of the landing phase (p=.05). Females went through 1.0° more hip abduction than males (p=.05), and used a smaller proportion of their gluteus maximus (p=.01) in both tasks. Examination of gluteal muscle contribution to individual and overall levels of functional valgus collapse in females revealed that at the 18% and 20% time points during the landing phase, less hip abduction strength and greater gluteus medius activation predicted greater peak hip adduction angles (R2 change = .10; p = .02) and higher external hip adduction moments (R2 change = .14, p = .06). Greater hip extension strength predicted greater peak hip abduction angles (R2 change = .08; p = .05), while greater gluteus maximus activation strengthened the prediction of greater initial (R2 change = .10, p = .03) and peak (R2 change = .14, p = .01) knee internal rotation angles. From 7% - 8% of the landing phase, greater external rotation ROM was associated with greater external hip adduction moment (R2 change = .18, p = .01). In males, less hip abduction strength strengthened the prediction of greater initial (R2 change = .12, p = .01) and peak knee internal rotation angles (R2 change = .14, p = .01), lesser peak knee external rotation angles (R2 change = .07, p =.09), and lesser peak knee abduction moments (R2 change = .06, p =.11). Less hip extension strength with greater gluteus maximus activation predicted greater peak hip external rotation moments (R2 change = .14, p = .01). Specifically from the 3% - 9% time points of the landing phase, greater hip extension strength was associated with greater knee abduction moment (R2 change = .17, p = .01) and less hip adduction moment (R2 change = .24, p = .001). At 0% and from 2% - 3% of the landing phase, greater internal and external rotation ROM were associated with greater knee abduction angle (R2 change = .27, p = .01) and greater hip adduction angle (R2 change = .23, p = .02). These results indicate that lower extremity biomechanics during a single-leg landing task are appreciably different than those observed during a double-leg landing task, and that a single-leg landing task elicits more profound sex differences, particularly during the early stage of single-leg load acceptance when ACL injuries are thought to occur (30-40ms post initial ground contact). As such, a single-leg landing task may be more appropriate for biomechanical screening of ACL injury risk. Gluteal strength and activation explained a unique proportion of variance in lower extremity biomechanics beyond what was explained by femoral alignment. In females, weaker gluteal muscles predicted riskier frontal plane hip kinematics. In males, gluteal function was more associated with kinetics. This implies that our male cohort used their musculature to create torque about a joint, whereas our female cohort was unable to create torque. Though femoral alignment (total ROM) explained considerably greater proportions of biomechanical variance than did gluteal function, observed associations between gluteal muscle function and biomechanics occurred 10-20ms after associations between femoral alignment and biomechanics. While the gluteal muscles may act mechanically independent of femoral alignment, it is possible that gluteal muscle function could be temporally linked to one’s femoral alignment. With these findings in mind, it may be beneficial for clinicians to implement gluteal strengthening programs and to encourage gluteal muscle pre-activation in individuals with excessive hip ROM to lessen their propensity for functional valgus collapse

Life-Expectancy Disparities Among Adults With HIV in the United States and Canada: The Impact of a Reduction in Drug- and Alcohol-Related Deaths Using the Lives Saved Simulation Model.

Improvements in life expectancy among people living with human immunodeficiency virus (PLWH) receiving antiretroviral treatment in the United States and Canada might differ among key populations. Given the difference in substance use among key populations and the current opioid epidemic, drug- and alcohol-related deaths might be contributing to the disparities in life expectancy. We sought to estimate life expectancy at age 20 years in key populations (and their comparison groups) in 3 time periods (2004-2007, 2008-2011, and 2012-2015) and the potential increase in expected life expectancy with a simulated 20% reduction in drug- and alcohol-related deaths using the novel Lives Saved Simulation model. Among 92,289 PLWH, life expectancy increased in all key populations and comparison groups from 2004-2007 to 2012-2015. Disparities in survival of approximately a decade persisted among black versus white men who have sex with men and people with (vs. without) a history of injection drug use. A 20% reduction in drug- and alcohol-related mortality would have the greatest life-expectancy benefit for black men who have sex with men, white women, and people with a history of injection drug use. Our findings suggest that preventing drug- and alcohol-related deaths among PLWH could narrow disparities in life expectancy among some key populations, but other causes of death must be addressed to further narrow the disparities

Binary Contamination in the SEGUE sample: Effects on SSPP Determinations of Stellar Atmospheric Parameters

Using numerical modeling and a grid of synthetic spectra, we examine the effects that unresolved binaries have on the determination of various stellar atmospheric parameters for SEGUE targets measured using the SEGUE Stellar Parameter Pipeline (SSPP). To model undetected binaries that may be in the SEGUE sample, we use a variety of mass distributions for the primary and secondary stars in conjunction with empirically determined relationships for orbital parameters to determine the fraction of G-K dwarf stars, as defined by SDSS color cuts, that will be blended with a secondary companion. We focus on the G-K dwarf sample in SEGUE as it records the history of chemical enrichment in our galaxy. To determine the effect of the secondary on the spectroscopic parameters, we synthesize a grid of model spectra from 3275 to 7850 K (~0.1 to 1.0 \msun) and [Fe/H]=-0.5 to -2.5 from MARCS model atmospheres using TurboSpectrum. We analyze both "infinite" signal-to-noise ratio (S/N) models and degraded versions, at median S/N of 50, 25 and 10. By running individual and combined spectra (representing the binaries) through the SSPP, we determine that ~10% of the blended G-K dwarf pairs with S/N>=25 will have their atmospheric parameter determinations, in particular temperature and metallicity, noticeably affected by the presence of an undetected secondary. To account for the additional uncertainty from binary contamination at a S/N~10, uncertainties of ~140 K and ~0.17 dex in [Fe/H] must be added in quadrature to the published uncertainties of the SSPP. (Abridged)Comment: 68 pages, 20 figures, 9 table

Conceptual framework on barriers and facilitators to implementing perinatal mental health care and treatment for women: the MATRIx evidence synthesis

Background: Perinatal mental health difficulties can occur during pregnancy or after birth and mental illness is a leading cause of maternal death. It is therefore important to identify the barriers and facilitators to implementing and accessing perinatal mental health care. Objectives: Our research objective was to develop a conceptual framework of barriers and facilitators to perinatal mental health care (defined as identification, assessment, care and treatment) to inform perinatal mental health services. Methods: Two systematic reviews were conducted to synthesise the evidence on: Review 1 barriers and facilitators to implementing perinatal mental health care; and Review 2 barriers to women accessing perinatal mental health care. Results were used to develop a conceptual framework which was then refined through consultations with stakeholders. Data sources: Pre-planned searches were conducted on MEDLINE, EMBASE, PsychInfo and CINAHL. Review 2 also included Scopus and the Cochrane Database of Systematic Reviews. Review methods: In Review 1, studies were included if they examined barriers or facilitators to implementing perinatal mental health care. In Review 2, systematic reviews were included if they examined barriers and facilitators to women seeking help, accessing help and engaging in perinatal mental health care; and they used systematic search strategies. Only qualitative papers were identified from the searches. Results were analysed using thematic synthesis and themes were mapped on to a theoretically informed multi-level model then grouped to reflect different stages of the care pathway. Results: Review 1 included 46 studies. Most were carried out in higher income countries and evaluated as good quality with low risk of bias. Review 2 included 32 systematic reviews. Most were carried out in higher income countries and evaluated as having low confidence in the results. Barriers and facilitators to perinatal mental health care were identified at seven levels: Individual (e.g. beliefs about mental illness); Health professional (e.g. confidence addressing perinatal mental illness); Interpersonal (e.g. relationship between women and health professionals); Organisational (e.g. continuity of carer); Commissioner (e.g. referral pathways); Political (e.g. women’s economic status); and Societal (e.g. stigma). These factors impacted on perinatal mental health care at different stages of the care pathway. Results from reviews were synthesised to develop two MATRIx conceptual frameworks of the (1) barriers and (2) facilitators to perinatal mental health care. These provide pictorial representations of 66 barriers and 39 facilitators that intersect across the care pathway and at different levels. Limitations: In Review 1 only 10% of abstracts were double screened and 10% of included papers methodologically appraised by two reviewers. The majority of reviews included in Review 2 were evaluated as having low (n = 14) or critically low (n = 5) confidence in their results. Both reviews only included papers published in academic journals and written in English. Conclusions: The MATRIx frameworks highlight the complex interplay of individual and system level factors across different stages of the care pathway that influence women accessing perinatal mental health care and effective implementation of perinatal mental health services. Recommendations for health policy and practice: These include using the conceptual frameworks to inform comprehensive, strategic and evidence-based approaches to perinatal mental health care; ensuring care is easy to access and flexible; providing culturally sensitive care; adequate funding of services; and quality training for health professionals with protected time to do it. Future work: Further research is needed to examine access to perinatal mental health care for specific groups, such as fathers, immigrants or those in lower income countries. Trial registration: This trial is registered as PROSPERO: (R1) CRD42019142854; (R2) CRD42020193107. Funding: This award was funded by the National Institute for Health and Care Research (NIHR) Health and Social Care Delivery Research programme (NIHR award ref: NIHR 128068) and is published in full in Health and Social Care Delivery Research; Vol. 12, No. 2. See the NIHR Funding and Awards website for further award information

The immediate effect of a balance wobble board protocol on knee and ankle joint position sense in female soccer players

Background: Lower limb injuries are widely recognized as the most prevalent injuries among female soccer players. Joint position sense plays a vital role in muscle reflexes, joint stability dynamics, and movement planning for neuromuscular control. Decreased accuracy in joint position sense can be considered an internal injury risk factor. Objective: The current study aims to investigate the immediate effect of a short-term balance protocol with a wobble board on knee and ankle joint position sense. Methods: Forty female participants were recruited and then randomly allocated into two groups: balance training (BTR; n = 20, age 23.50 ± 1.50 years) and control (CON; n = 20, age 23.10 ± 1.77 years). Knee and ankle joint reconstruction errors were measured using a gyroscope at 60° of knee flexion and 30° of ankle plantarflexion. Following this, the BTR group participated in a short-term balance protocol (one session). Immediately following training and then one hour later, the reconstruction error was measured in both groups. Results: A mixed-repeated measures analysis of variance demonstrated that for the BTR group, the absolute angular error (AAE) before and after intervention decreased by 2.14° and 2.95° in the knee (p = .001) and ankle (p = .001) joints, respectively. In addition, an hour after intervention, the AAE remained below the initial value in the two joints (p = .001). Specifically, in the CON group, the AAE in the knee joint did not show a significant decrease, and similarly, no significant change was observed in the AAE in the ankle joint, and also an hour after the intervention. Conclusions: A wobble board training session may stimulate the sensory receptors of the knee and ankle joints of female amateur soccer players and increased joint position sense accuracy and is present one hour post intervention

Doves and hawks in economics revisited. An evolutionary quantum game theory-based analysis of financial crises

The last financial and economic crisis demonstrated the dysfunctional long-term effects of aggressive behaviour in financial markets. Yet, evolutionary game theory predicts that under the condition of strategic dependence a certain degree of aggressive behaviour remains within a given population of agents. However, as the consequences of the financial crisis exhibit, it would be desirable to change the 'rules of the game' in a way that prevents the occurrence of any aggressive behaviour and thereby also the danger of market crashes. The paper picks up this aspect. Through the extension of the in literature well-known Hawk-Dove game by a quantum approach, we can show that dependent on entanglement, also evolutionary stable strategies can emerge, which are not predicted by classical evolutionary game theory and where the total economic population uses a non aggressive quantum strategy

A Photometric Metallicity Estimate of the Virgo Stellar Overdensity

We determine photometric metal abundance estimates for individual main-sequence stars in the Virgo Overdensity (VOD), which covers almost 1000 deg^2 on the sky, based on a calibration of the metallicity sensitivity of stellar isochrones in the gri filter passbands using field stars with well-determined spectroscopic metal abundances. Despite the low precision of the method for individual stars, we derive [Fe/H] = -2.0 +/-0.1 (internal) +/-0.5 (systematic) for the metal abundance of the VOD from photometric measurements of 0.7 million stars in the Northern Galactic hemisphere with heliocentric distances from ~10 kpc to ~20 kpc. The metallicity of the VOD is indistinguishable, within Delta [Fe/H] < 0.2, from that of field halo stars covering the same distance range. This initial application suggests that the SDSS gri passbands can be used to probe the properties of main-sequence stars beyond ~10 kpc, complementing studies of nearby stars from more metallicity-sensitive color indices that involve the u passband.Comment: 5 pages, 3 figures, Accepted for publication in ApJ Letter