The Formation of Fragments at Corotation in Isothermal Protoplanetary Disks

Numerical hydrodynamics simulations have established that disks which are evolved under the condition of local isothermality will fragment into small dense clumps due to gravitational instabilities when the Toomre stability parameter $Q$ is sufficiently low. Because fragmentation through disk instability has been suggested as a gas giant planet formation mechanism, it is important to understand the physics underlying this process as thoroughly as possible. In this paper, we offer analytic arguments for why, at low $Q$, fragments are most likely to form first at the corotation radii of growing spiral modes, and we support these arguments with results from 3D hydrodynamics simulations.Comment: 21 pages, 1 figur

Strain-facilitated process for the lift-off of a Si layer of less than 20 nm thickness

We report a process for the lift-off of an ultrathin Si layer. By plasma hydrogenation of a molecular-beam-epitaxy-grown heterostructure of SiSb-doped-SiSi, ultrashallow cracking is controlled to occur at the depth of the Sb-doped layer. Prior to hydrogenation, an oxygen plasma treatment is used to induce the formation of a thin oxide layer on the surface of the heterostructure. Chemical etching of the surface oxide layer after hydrogenation further thins the thickness of the separated Si layer to be only 15 nm. Mechanisms of hydrogen trapping and strain-facilitated cracking are discussed

Quantum walk on distinguishable non-interacting many-particles and indistinguishable two-particle

We present an investigation of many-particle quantum walks in systems of non-interacting distinguishable particles. Along with a redistribution of the many-particle density profile we show that the collective evolution of the many-particle system resembles the single-particle quantum walk evolution when the number of steps is greater than the number of particles in the system. For non-uniform initial states we show that the quantum walks can be effectively used to separate the basis states of the particle in position space and grouping like state together. We also discuss a two-particle quantum walk on a two- dimensional lattice and demonstrate an evolution leading to the localization of both particles at the center of the lattice. Finally we discuss the outcome of a quantum walk of two indistinguishable particles interacting at some point during the evolution.Comment: 8 pages, 7 figures, To appear in special issue: "quantum walks" to be published in Quantum Information Processin

Where’s the “Everyday Black Woman”? An intersectional qualitative analysis of Black Women’s decision-making regarding HIV pre-exposure prophylaxis (PrEP) in Mississippi

Background: Black cisgender women in the U.S. South bear a disproportionate burden of HIV compared to cisgender women in other racial and ethnic groups and in any other part of the US. Critical to decreasing new HIV infections is the improved delivery of pre-exposure prophylaxis (PrEP) for Black cisgender women as it remains underutilized in 2021. Informed by intersectionality, the study sought to characterize the sociostructural influences on Black cisgender women’s deliberations about PrEP within the context of interlocking systems of oppression including racism, sexism, and classism. Methods: Six focus groups were conducted with 37 Black women residing in Jackson, Mississippi. This sample was purposively recruited to include Black cisgender women who were eligible for PrEP but had never received a PrEP prescription. Results: Six themes were identified as concerns during PrEP deliberation among Black women: 1) limited PrEP awareness, 2) low perceived HIV risk, 3) concerns about side effects, 4) concerns about costs, 5) limited marketing, and 6) distrust in the healthcare system. Three themes were identified as facilitators during PrEP deliberations: 1) women’s empowerment and advocacy, 2) need for increased PrEP-specific education, and 3) the positive influence of PrEP-engaged women’s testimonials. Black women shared a limited awareness of PrEP exacerbated by the lack of Black women-specific marketing. Opportunities to support Black women-specific social marketing could increase awareness and knowledge regarding PrEP’s benefits and costs. Black women also shared their concerns about discrimination in healthcare and distrust, but they felt that these barriers may be addressed by patient testimonials from PrEP-engaged Black women, empowerment strategies, and directly addressing provider biases. Conclusions: An effective response to PrEP implementation among Black women in the South requires developing programs to center the needs of Black women and carry out active strategies that prioritize peer advocacy while reinforcing positive and mitigating negative influences from broader social and historical contexts

“PrEP’s just to secure you like insurance”: a qualitative study on HIV pre-exposure prophylaxis (PrEP) adherence and retention among black cisgender women in Mississippi

Background: Pre-exposure prophylaxis (PrEP) has the potential to reduce transmission of HIV among Black cisgender women in the Southern United States (U.S.); however, national data suggests that PrEP initiation is lowest in the South and among Black women compared to other U.S. regions and white women. This study applied intersectionality and PrEP multilevel resilience frameworks to assess how socio-structural and clinical contexts shaped PrEP persistence among Black cisgender women in Mississippi. Methods: Semi-structured interviews were conducted with eight Black cisgender women in Jackson, Mississippi. This sample was purposively recruited to include PrEP-initiated Black cisgender women. Results: Six themes identified that shaped PrEP care among Black cisgender women: (1) internal assets, (2) sole responsibility to HIV prevention, (3) added protection in HIV serodifferent relationships, (4) financial issues, (5) trust and distrust in the medical system, and (6) side effects. Black cisgender women reported that PrEP persistence increased control over their sexual health, reduced anxiety about HIV, and promoted self-care. Black cisgender women also indicated that medication assistance programs increased PrEP affordability resulting in continued persistence. Conclusions: In addition to preventing HIV, PrEP may yield secondary positive impacts on the health and relationships of Black cisgender women. However, very few Black cisgender women in the South are using PrEP given intersectional barriers and thus necessitates adaptive strategies to support PrEP initiation and persistence. Efforts aimed at increasing the coverage of PrEP among Black cisgender women should consider implementation strategies responsive to lived realities of Black women

Evaluating Forest Growth Models

Effective model evaluation is not a single, simple procedure, but comprises several interrelated steps that cannot be separated from each other or from the purpose and process of model construction. We draw attention to several statistical and graphical procedures that may assist in model calibration and evaluation, with special emphasis on those useful in forest growth modelling. We propose a five-step framework to examine logic and bio-logic, statistical properties, characteristics of errors, residuals, and sensitivity analyses. Empirical evaluations may be made both with data used in fitting the model, and with additional data not previously used. We emphasize that the validity of conclusions drawn from all these assessments depends on the validity of assumptions underlying both the model and the evaluation. These principles should be kept in mind throughout model construction and evaluation

Synthetic approaches to pallimamine and analogues using direct imine acylation

The use of Direct Imine Acylation (DIA) methodology for the total synthesis of pallimamine is described, with three different synthetic routes examined. The construction of three advanced δ-lactam precursors, all utilising DIA, is described, along with attempts to progress these compounds further, using three distinct desymmetrisation strategies, two involving alcohol-aryl coupling, and a third involving an unusual diastereoselective lactonisation

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter