Machine learning the dimension of a Fano variety.

Fano varieties are basic building blocks in geometry - they are 'atomic pieces' of mathematical shapes. Recent progress in the classification of Fano varieties involves analysing an invariant called the quantum period. This is a sequence of integers which gives a numerical fingerprint for a Fano variety. It is conjectured that a Fano variety is uniquely determined by its quantum period. If this is true, one should be able to recover geometric properties of a Fano variety directly from its quantum period. We apply machine learning to the question: does the quantum period of X know the dimension of X? Note that there is as yet no theoretical understanding of this. We show that a simple feed-forward neural network can determine the dimension of X with 98% accuracy. Building on this, we establish rigorous asymptotics for the quantum periods of a class of Fano varieties. These asymptotics determine the dimension of X from its quantum period. Our results demonstrate that machine learning can pick out structure from complex mathematical data in situations where we lack theoretical understanding. They also give positive evidence for the conjecture that the quantum period of a Fano variety determines that variety.

Databases of quantum periods for Fano manifolds.

Fano manifolds are basic building blocks in geometry - they are, in a precise sense, atomic pieces of shapes. The classification of Fano manifolds is therefore an important problem in geometry, which has been open since the 1930s. One can think of this as building a Periodic Table for shapes. A recent breakthrough in Fano classification involves a technique from theoretical physics called Mirror Symmetry. From this perspective, a Fano manifold is encoded by a sequence of integers: the coefficients of a power series called the regularized quantum period. Progress to date has been hindered by the fact that quantum periods require specialist expertise to compute, and descriptions of known Fano manifolds and their regularized quantum periods are incomplete and scattered in the literature. We describe databases of regularized quantum periods for Fano manifolds in dimensions up to four. The databases in dimensions one, two, and three are complete; the database in dimension four will be updated as new four-dimensional Fano manifolds are discovered and new regularized quantum periods computed.

Maximally mutable Laurent polynomials.

We introduce a class of Laurent polynomials, called maximally mutable Laurent polynomials (MMLPs), which we believe correspond under mirror symmetry to Fano varieties. A subclass of these, called rigid, are expected to correspond to Fano varieties with terminal locally toric singularities. We prove that there are exactly 10 mutation classes of rigid MMLPs in two variables; under mirror symmetry these correspond one-to-one with the 10 deformation classes of smooth del Pezzo surfaces. Furthermore, we give a computer-assisted classification of rigid MMLPs in three variables with reflexive Newton polytope; under mirror symmetry these correspond one-to-one with the 98 deformation classes of three-dimensional Fano manifolds with very ample anti-canonical bundle. We compare our proposal to previous approaches to constructing mirrors to Fano varieties, and explain why mirror symmetry in higher dimensions necessarily involves varieties with terminal singularities. Every known mirror to a Fano manifold, of any dimension, is a rigid MMLP.

Management of Australian Patients with Severe Traumatic Brain Injury: Are Potentially Harmful Treatments Still Used?

Clinical trials have shown that intravenous albumin and decompressive craniectomy to treat early refractory intracranial hypertension can cause harm in patients with severe traumatic brain injury (TBI). The extent to which these treatments remain in use is unknown. We conducted a multi-center retrospective cohort study of adult patients with severe TBI admitted to five neurotrauma centers across Australia between April 2013 and March 2015. Patients were identified from local trauma and intensive care unit (ICU) registries and followed until hospital discharge. Main outcome measures were the administration of intravenous albumin, and decompressive craniectomy for intracranial hypertension. Analyses were predominantly descriptive. There were 303 patients with severe TBI, of whom a minority received albumin (6.9%) or underwent early decompressive craniectomy for treatment of refractory intracranial hypertension complicating diffuse TBI (2.3%). The median (intequartile range [IQR]) age was 35 (24, 58), and most injuries were caused by road traffic accidents (57.4%) or falls (25.1%). Overall, 34.3% of patients died while in the hospital and the remainder were discharged to rehabilitation (44.6%), other health care facilities (4.6%), or home (16.5%). There were no patient characteristics significantly associated with use of albumin or craniectomy. Intravenous albumin and craniectomy for treatment of intracranial hypertension were used infrequently in Australian neurotrauma centers, indicating alignment between best available evidence and practice.

'My Tablets are on Top of the Fridge': The Roles of Relationship Desire and Medical Mistrust in ART Adherence for HIV-Positive MSM and Transgender Women Living in Rural South Africa.

Given the high HIV prevalence for men who have sex with men (MSM) and transgender women in South Africa, there is limited understanding of social determinants that influence antiretroviral treatment (ART) adherence. Although universal testing and treatment (UTT) is available, ART adherence remains suboptimal. We conducted focus groups with MSM and transgender women in order to understand factors influencing their ART adherence in Mpumalanga, South Africa. All focus groups were audio-recorded, transcribed and translated for analysis using a constant comparison approach, guided by the concept of Therapeutic Citizenship. We found there is medical mistrust of ART based on differing interpretations of HIV cure that may influence treatment adherence behaviors within social networks, and relationship desire had a significant influence on optimal ART adherence. Our findings suggest that clinics must provide interventions that integrate HIV disclosure and relationship skill-building to support optimal ART adherence for MSM and transgender women under UTT.

"Booze is the main factor that got me where I am today": alcohol use and HIV risk for MSM in rural South Africa.

Excessive alcohol consumption has been shown to increase HIV risk for men who have sex with men (MSM) and compromise HIV prevention behaviors. However, there is limited contextual understanding of alcohol use for MSM in rural sub-Saharan African settings, which can inform and direct HIV interventions. Applying an adaptation of PhotoVoice, we worked with 35 HIV-positive MSM who created photo-essays about alcohol and HIV in Mpumalanga. A semi-structured protocol was used in focus group discussions that were audio-recorded, translated and transcribed. Transcript data and visual data of 24 photo-essays were analyzed using a constant comparison approach. We found that participants used alcohol to build and sustain social networks, meet sexual partners, and enhance sexual experience. Excessive alcohol use was common, which was associated with increased HIV risk behaviors within a community of MSM who maintained multiple partnerships. Our study suggests that HIV interventions need to address excessive alcohol use to mitigate the associated HIV risk at both the individual and community levels.

Exploring dual disclosures for men who have sex with men in Mpumalanga, South Africa: a report from the field.

We explored to whom rural men who have sex with men (MSM) disclose their sexual identity and HIV status in Mpumalanga, South Africa. Participants were recruited using a modified snowball sampling method in order to complete a questionnaire. Descriptive and logistic regression analyses were conducted. There were 47 participants of whom 22 self-reported as HIV-positive. Most participants disclosed their sexuality and HIV status to immediate family members and gay-identified friends. We found that the longer someone had identified as MSM, the more likely they were to be HIV-positive and not go to clinic. Education and employment modified these findings. This study presents a broader picture of MSM in this rural African setting: that they do disclose their sexuality and HIV status to others in their community. However, more research is needed to develop these measures. We need to assess how long participants identify as MSM, how long they have been HIV-positive, and to whom they have disclosed these aspects of their lives to inform HIV prevention and treatment interventions for MSM in rural settings.

Exploring the Impact of Childhood Abuse on HIV Social and Attitudinal Factors Among Adults With and Without this History in Sub-Saharan Africa: Findings from NIMH Project Accept (HPTN 043).

Using data from four sites in three African countries, this community randomized study examined the association between childhood sexual and/or physical abuse (CSA and/or CPA) and HIV disclosure, HIV-related stigma, stress, and social support among adults with and without a history of abuse. A history of abuse among men was associated with higher levels of adult-reported stress and HIV-related stigma, and with significantly lower rates of HIV test result disclosure to current partners. Women with a history of CSA and/or CPA had significantly higher perceived stigma, discrimination and stress. Although childhood abuse was significantly associated with adult stress and stigmatization, participants with histories of CSA and/or CPA also reported significantly higher perceived social support compared to people without such experiences. These findings may reflect support received in response to disclosure of CSA or CPA or emotional ambivalence in relationships that have been found to be associated with child abuse. We conclude that it is critical for HIV prevention interventions to advocate for the primary prevention of child abuse, for early identification of adolescents and adults who report experiencing childhood abuse, and to address stigma and stress-related attitudinal, behavioral and relationship difficulties experiences as an aftermath of early abuse that increase their risk of HIV.

Acute temperature sensitivity in optic nerve axons explained by an electrogenic membrane potential.

Classical work in squid axon reports resting membrane potential is independent of temperature, but our findings suggest that this is not the case for axons in mammalian optic nerve. Refractory period duration changes over 10 times between 37 °C and room temperature, and afterpotential polarity is also acutely temperature sensitive, inconsistent with changes in temperature impacting nerve function only through altered rates of ion channel gating kinetics. Our evidence suggests that the membrane potential is enhanced by warming, an effect reduced by exposure to ouabain. The temperature dependence can be explained if axonal Na(+)/K(+) ATPase continuously expels Na(+) ions that enter axons largely electroneutrally, thereby adding a substantial electrogenic component to the membrane potential. Block of the Na(+) transporter NKCC1 with bumetanide increases refractoriness, like depolarization, indicating that this is a probable route by which Na(+) enters, raising the expectation that the rate of electroneutral Na(+) influx increases with temperature and suggesting a temperature-dependent transmembrane Na(+) cycle that contributes to membrane potential.

Pulmonary hypertension in well-transfused thalassemia major patients.

The risk for pulmonary hypertension (PH) in thalassemia major (TM) patients remains controversial. We report echocardiography results from 60 TM patients: we evaluated the association between tricuspid regurgitation velocities (TRV), iron stores, and serologic markers of hemolysis and arginine dysregulation. Patients were enrolled from August 2004 until May 2009. All parameters were inversely weighted by the number of exams. TRV was comparable between sexes and it was uncorrelated with age. At the first exam, TR velocities at the upper limits of normal (2.5-2.7m/s) were observed in 8 patients. An abnormal TRV (2.9m/s) was found in 1 patient. Borderline increases in TRV were associated with a reduced global arginine bioavailability (R=-0.399 P=0.005), increased anemia (hemoglobin: R=-0.219 P=0.0461), cardiac index (R=0.223 P=0.0481), and diastolic dysfunction (E/A: R=0.289 P=0.0088; E/E': R=0.223 P=0.0453), but not hemolysis, iron overload and systolic function evaluated by Magnetic Resonance Imaging, and splenectomy. Well-transfused TM patients have a lower risk for PH than thalassemia intermedia patients. However, they do have vascular stressors that raise their lifetime PH risk to levels higher than for the general population. Consequently, we support recommendations for annual echocardiographic screening and cardiac catheterization for persistent TRV above 3m/s.

Reported physical and sexual abuse in childhood and adult HIV risk behaviour in three African countries: findings from Project Accept (HPTN-043).

Childhood sexual and physical abuse have been linked to adolescent and adult risky sexual behaviors, including early sexual debut, an increased number of sexual partners, unprotected sex, alcohol and drug use during sex and sexual violence. This paper explores these relationships among both men and women who report histories of childhood abuse from representative samples of communities in three countries in southern and eastern Africa (South Africa, Zimbabwe and Tanzania). Data were collected as part of a 3-year randomized community trial to rapidly increase knowledge of HIV status and to promote community responses through mobilisation, mobile testing, provision of same-day HIV test results and post-test support for HIV. The results indicate that reported childhood sexual and physical abuse is high in all three settings, also among men, and shows strong relationships with a range of sexual risk behaviors, including age at first sex (OR -0.6 (CI: -0.9, -0.4, p < 0.003)-among men, OR -0.7 (CI: -0.9, -0.5, p < 0.001)-among women), alcohol (OR 1.43 (CI: 1.22, 1.68, p < 0.001)-men, OR 1.83 (CI: 1.50, 2.24, p < 0.001)-women) and drug use (OR 1.65 (CI: 1.38, 1.97, p < 0.001)-men, OR 3.14 (CI: 1.95, 5.05, p < 0.001)-women) and two forms of partner violence-recent forced sex (OR 2.22 (CI: 1.66, 2.95, p < 0.001)-men, OR 2.76 (CI: 2.09, 3.64, p < 0.001)-women) and ever being hurt by a partner (OR 3.88 (CI: 2.84, 5.29, p < 0.001)-men, OR 3.06 (CI: 2.48, 3.76, p < 0.001)-women). Individuals abused in childhood comprise between 6 and 29 % of young adult men and women living in these African settings and constitute a population at high risk of HIV infection.

Influence of terminal RPE on session RPE.

Session rating of perceived exertion (RPE; SRPE), a convenient model for monitoring the overall perceived exertion of an exercise bout, is not well understood. The SRPE may be linked to final acute RPE before exercise cessation. This study investigated the potential link between terminal acute RPE (TRPE) and the SRPE using cycling trials of equated work. Fifteen subjects (age: 24.3 ± 5.1 years) completed a maximal exertion cycle trial followed by 2 (counterbalanced) 40-minute cycling trials at approximately 75% of individualized V[Combining Dot Above]O2max. By manipulating warm-up and cooldown, the trials were designed to result in a high TRPE (HITRPE) and low TRPE (LOTRPE). The heart rate (HR) and RPE were recorded every 5 minutes during exercise, with the SRPE recorded 20 minutes postexercise. The mean RPE (MeanRPE) during exercise (min 10-40 HITRPE and minutes 5-35 for LOTRPE) was calculated by averaging all RPE responses recorded during exercise at 75% V[Combining Dot Above]O2max. Two-way (trial × time) repeated measures analysis of variance and Bonferroni post hoc tests were used to compare the MeanRPE, SRPE, and TRPE. MeanRPE, HR, and power output (using paired t-test) for exercise at 75% V[Combining Dot Above]O2max did not differ (p > 0.05) between HITRPE and LOTRPE. The TRPE at minute 40 was significantly lower (p < 0.05) for LOTRPE (3.1 ± 2.6) vs. HITRPE (8.2 ± 1.7), no significant difference was found for SRPE (LOTRPE: 7.6 ± 2.0 vs. HITRPE 7.4 ± 1.7). The findings indicate that the SRPE was not linked to TRPE. Further research is warranted using various modalities to extend the understanding of potential mediating factors of SRPE.

Relationship between alcohol consumption prior to sex, unprotected sex and prevalence of STI/HIV among socially marginalized men in three coastal cities of Peru.

This article presents data about the relationship between alcohol consumption prior to sex and unprotected sex and the prevalence of at least one sexually transmitted infection (STI) including HIV among socially marginalized men in three coastal Peruvians cities. During an epidemiological survey with 2,146 men, we assessed their STI prevalence, frequency of alcohol consumption prior to sex, unprotected sex and other sexual risk behaviors. The overall prevalence of at least one STI/HIV was 8.5 % (95 % CI 7.3-9.7), the prevalence of unprotected sex was 79.1 % (95 % CI 77.8-80.3) and alcohol consumption prior to sex with any of the last five sex partners in the previous 6 months was 68.9 % (95 % CI 66.9-70.9). Bivariate and multivariate analysis showed that alcohol consumption of participants or their partners prior to sex were associated with the prevalence of at least one STI, adjusted Prevalence Ratio (aPR) = 1.3 (95 % CI 1.01-1.68). Unprotected sex was significantly associated with alcohol consumption prior to sex when both partners used alcohol, aPR = 1.15 (95 % CI 1.10-1.20) or when either one of them used alcohol aPR = 1.14 (95 % CI 1.09-1.18). These findings concur with previous literature suggesting a relationship between alcohol consumption prior to sex and STI and HIV. These data improve our understanding of this relationship in this context and could be used to enhance STI and HIV prevention strategies for socially marginalized men in Peru.

"You must do the test to know your status": attitudes to HIV voluntary counseling and testing for adolescents among South African youth and parents.

Reduced HIV risk behavior and increased use of care and support services have been demonstrated among adults accessing HIV voluntary counseling and testing (VCT). The impact of VCT on adolescents is, however, not known. Focus group discussions were held with adolescents and parents in two South African townships to establish the perceptions of and needs for VCT among young people. Ecological theory informed the analysis. Adolescents had limited experience of VCT, were afraid of knowing their HIV status, and felt that testing was only for symptomatic individuals. Youth felt that they would disclose their HIV status to family members who they felt would be most supportive. Youth were afraid of stigma and discrimination; rarely referring to the community as a source of support. Discussions highlighted the inappropriateness of clinical facilities for youth VCT. We conclude with recommendations for youth-friendly VCT services.