221 research outputs found
On All-loop Integrands of Scattering Amplitudes in Planar N=4 SYM
We study the relationship between the momentum twistor MHV vertex expansion
of planar amplitudes in N=4 super-Yang-Mills and the all-loop generalization of
the BCFW recursion relations. We demonstrate explicitly in several examples
that the MHV vertex expressions for tree-level amplitudes and loop integrands
satisfy the recursion relations. Furthermore, we introduce a rewriting of the
MHV expansion in terms of sums over non-crossing partitions and show that this
cyclically invariant formula satisfies the recursion relations for all numbers
of legs and all loop orders.Comment: 34 pages, 17 figures; v2: Minor improvements to exposition and
discussion, updated references, typos fixe
A Universal Model of Global Civil Unrest
Civil unrest is a powerful form of collective human dynamics, which has led
to major transitions of societies in modern history. The study of collective
human dynamics, including collective aggression, has been the focus of much
discussion in the context of modeling and identification of universal patterns
of behavior. In contrast, the possibility that civil unrest activities, across
countries and over long time periods, are governed by universal mechanisms has
not been explored. Here, we analyze records of civil unrest of 170 countries
during the period 1919-2008. We demonstrate that the distributions of the
number of unrest events per year are robustly reproduced by a nonlinear,
spatially extended dynamical model, which reflects the spread of civil disorder
between geographic regions connected through social and communication networks.
The results also expose the similarity between global social instability and
the dynamics of natural hazards and epidemics.Comment: 8 pages, 3 figure
Counting Exceptional Instantons
We show how to obtain the instanton partition function of N=2 SYM with
exceptional gauge group EFG using blow-up recursion relations derived by
Nakajima and Yoshioka. We compute the two instanton contribution and match it
with the recent proposal for the superconformal index of rank 2 SCFTs with E6,
E7 global symmetry.Comment: 16 pages, references adde
Solution to the Ward Identities for Superamplitudes
Supersymmetry and R-symmetry Ward identities relate on-shell amplitudes in a
supersymmetric field theory. We solve these Ward identities for (Next-to)^K MHV
amplitudes of the maximally supersymmetric N=4 and N=8 theories. The resulting
superamplitude is written in a new, manifestly supersymmetric and R-invariant
form: it is expressed as a sum of very simple SUSY and SU(N)_R-invariant
Grassmann polynomials, each multiplied by a "basis amplitude". For (Next-to)^K
MHV n-point superamplitudes the number of basis amplitudes is equal to the
dimension of the irreducible representation of SU(n-4) corresponding to the
rectangular Young diagram with N columns and K rows. The linearly independent
amplitudes in this algebraic basis may still be functionally related by
permutation of momenta. We show how cyclic and reflection symmetries can be
used to obtain a smaller functional basis of color-ordered single-trace
amplitudes in N=4 gauge theory. We also analyze the more significant reduction
that occurs in N=8 supergravity because gravity amplitudes are not ordered. All
results are valid at both tree and loop level.Comment: 29 pages, published versio
'Thinking like a fish': adaptive strategies for coping with vulnerability and variability emerging from a relational engagement with kob
Based on ethnographic fieldwork amongst a group of commercial handline fishers in the town of Stilbaai in South Africa's southern Cape region, this paper presents a range of flexible, adaptive and evolving strategies through which fishers negotiate constantly shifting variability in weather patterns, fish stocks, fisheries policies, and economic conditions. These variabilities constitute a diverse set of vulnerabilities to which fishers must respond in order to sustain their livelihoods. In this context, the act of 'thinking like a fish' on the part of the fishers provides them with an effective means of adapting to variability and uncertainty. Findings of ethnographic research in 2010-11 suggest that a number of the fishers who participated in the research actively work towards achieving a balance between profit and sustainability. 'Thinking like a fish' is an embodied, interactive way of knowing that emerges from interactions between fishers and fish, offering an ethical and ecological outlook which is a valuable resource for fisheries and conservation management in the region. We suggest that the deeply embodied interactional component of 'thinking like a fish' results from a desire to understand the life world of fish and to think from their perspective in order to more effectively target them while sustaining the species and ecosystem
Disparities and risks of sexually transmissible infections among men who have sex with men in China: a meta-analysis and data synthesis.
BACKGROUND: Sexually transmitted infections (STIs), including Hepatitis B and C virus, are emerging public health risks in China, especially among men who have sex with men (MSM). This study aims to assess the magnitude and risks of STIs among Chinese MSM. METHODS: Chinese and English peer-reviewed articles were searched in five electronic databases from January 2000 to February 2013. Pooled prevalence estimates for each STI infection were calculated using meta-analysis. Infection risks of STIs in MSM, HIV-positive MSM and male sex workers (MSW) were obtained. This review followed the PRISMA guidelines and was registered in PROSPERO. RESULTS: Eighty-eight articles (11 in English and 77 in Chinese) investigating 35,203 MSM in 28 provinces were included in this review. The prevalence levels of STIs among MSM were 6.3% (95% CI: 3.5-11.0%) for chlamydia, 1.5% (0.7-2.9%) for genital wart, 1.9% (1.3-2.7%) for gonorrhoea, 8.9% (7.8-10.2%) for hepatitis B (HBV), 1.2% (1.0-1.6%) for hepatitis C (HCV), 66.3% (57.4-74.1%) for human papillomavirus (HPV), 10.6% (6.2-17.6%) for herpes simplex virus (HSV-2) and 4.3% (3.2-5.8%) for Ureaplasma urealyticum. HIV-positive MSM have consistently higher odds of all these infections than the broader MSM population. As a subgroup of MSM, MSW were 2.5 (1.4-4.7), 5.7 (2.7-12.3), and 2.2 (1.4-3.7) times more likely to be infected with chlamydia, gonorrhoea and HCV than the broader MSM population, respectively. CONCLUSION: Prevalence levels of STIs among MSW were significantly higher than the broader MSM population. Co-infection of HIV and STIs were prevalent among Chinese MSM. Integration of HIV and STIs healthcare and surveillance systems is essential in providing effective HIV/STIs preventive measures and treatments. TRIAL REGISTRATION: PROSPERO NO: CRD42013003721
Selberg Integral and SU(N) AGT Conjecture
An intriguing coincidence between the partition function of super Yang-Mills
theory and correlation functions of 2d Toda system has been heavily studied
recently. While the partition function of gauge theory was explored by
Nekrasov, the correlation functions of Toda equation have not been completely
understood. In this paper, we study the latter in the form of Dotsenko-Fateev
integral and reduce it in the form of Selberg integral of several Jack
polynomials. We conjecture a formula for such Selberg average which satisfies
some consistency conditions and show that it reproduces the SU(N) version of
AGT conjecture.Comment: 35 pages, 5 figures; v2: minor modifications; v3: typos corrected,
references adde
Bryozoans are Major Modern Builders of South Atlantic Oddly Shaped Reefs
Supplementary information accompanies this paper at https://doi.org/10.1038/s41598-018-27961-6.In major modern reef regions, either in the Indo-Pacific or the Caribbean, scleractinian corals are
described as the main reef framework builders, often associated with crustose coralline algae. We
used underwater cores to investigate Late Holocene reef growth and characterise the main framework
builders in the Abrolhos Shelf, the largest and richest modern tropical reef complex in the South
Western Atlantic, a scientifically underexplored reef province. Rather than a typical coralgal reef,
our results show a complex framework building system dominated by bryozoans. Bryozoans were
major components in all cores and age intervals (2,000 yrs BP), accounting for up to 44% of the reef
framework, while crustose coralline algae and coral accounted for less than 28 and 23%, respectively.
Reef accretion rates varied from 2.7 to 0.9 mm yr−1, which are similar to typical coralgal reefs.
Bryozoan functional groups encompassed 20 taxa and Celleporaria atlantica (Busk, 1884) dominated
the framework at all cores. While the prevalent mesotrophic conditions may have driven suspensionfeeders’
dominance over photoautotrophs and mixotrophs, we propose that a combination of historical
factors with the low storm-disturbance regime of the tropical South Atlantic also contributed to the
region’s low diversity, and underlies the unique mushroom shape of the Abrolhos pinnacles.We thank CNPq/FAPES-Sisbiota/PELD, CAPES/IODP, CAPES/Ciências do Mar, and ANP/Brasoil for long
term project funding. We also thank ICMBio for research permits and field logistic support, and Conservation
International for providing and authorizing the use of the IKONOS image. JMW and JCB are International
Visiting Researcher at UFES and JBRJ, supported by the Science Without Borders program. Zá Cajueiro
provided invaluable field support and Ronaldo Francini, Carlos Janovitch and Lucio Engler helped in the drilling
operations. This is a contribution from the Rede Abrolhos (abrolhos.org)
Concurrent validity of self-rating scale of self-directed learning and self-directed learning instrument among Italian nursing students
BACKGROUND: Self-Directed Learning develops when students take the initiative for their learning, recognising needs, formulating goals, identifying resources, implementing appropriate strategies and evaluating learning outcomes. This should be seen as a collaborative process between the nurse educator and the learner. At the international level, various instruments have been used to measure Self-Directed Learning abilities (SDL), both in original and in culturally-adapted versions. However, few instruments have been subjected to full validation, and no gold standard reference has been established to date. In addition, few researchers have adopted the established tools to assess the concurrent validity of the emerging new tools. Therefore, the aim of this study was to measure the concurrent validity between the Self-Rating Scale of Self-Directed Learning (SRSSDL_Ita) - Italian version and the Self-Directed Learning Instruments (SDLI) in undergraduate nursing students.
METHODS: A concurrent validity study design was conducted in a Bachelor level nursing degree programme located in Italy. All nursing students attending the first, second or third year (n=428) were the target sample. The SRSSDL_Ita, and the SDLI were used. The Pearson correlation was used to determine the concurrent validity between the instruments; the confidence of intervals (CI 95%) bias-corrected and accelerated bootstrap (BCa), were also calculated.
RESULTS: The majority of participants were students attending their first year (47.9%), and were predominately female (78.5%). Their average age was 22.5\ub14.1. The SDL abilities scores, as measured with the SRSSDL_Ita (min 40, max 200), were, on average, 160.79 (95% CI 159.10-162.57; median 160); while with the SDLI (min 20, max 100), they were on average 82.57 (95% CI 81.79-83.38; median 83). The Pearson correlation between the SRSSDL_Ita and SDLI instruments was 0.815 (CI BCa 95% 0.774-0.848), (p=0.000).
CONCLUSIONS: The findings confirm the concurrent validity of the SRSSDL_Ita with the SDLI. The SRSSDL_Ita instrument can be useful in the process of identifying Self-Directed Learning abilities, which are essential for students to achieve the expected learning goals and become lifelong learners
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