16,140 research outputs found
On the structure of the BBGKY hierarchy for a Boltzmann gas
Structure of BBGKY hierarchy for Boltzmann gas and particle distribution
A computer program for the calculation of laminar and turbulent boundary layer flows
The results are presented of a study to produce a computer program to calculate laminar and turbulent boundary layer flows. The program is capable of calculating the following types of flow: (1) incompressible or compressible, (2) two dimensional or axisymmetric, and (3) flows with significant transverse curvature. Also, the program can handle a large variety of boundary conditions, such as blowing or suction, arbitrary temperature distributions and arbitrary wall heat fluxes. The program has been specialized to the calculation of equilibrium air flows and all of the thermodynamic and transport properties used are for air. For the turbulent transport properties, the eddy viscosity approach has been used. Although the eddy viscosity models are semi-empirical, the model employed in the program has corrections for pressure gradients, suction and blowing and compressibility. The basic method of approach is to put the equations of motion into a finite difference form and then solve them by use of a digital computer. The program is written in FORTRAN 4 and requires small amounts of computer time on most scientific machines. For example, most laminar flows can be calculated in less than one minute of machine time, while turbulent flows usually require three or four minutes
Electrostatic Tuning of the Superconductor-Insulator Transition in Two Dimensions
Superconductivity has been induced in insulating ultra-thin films of
amorphous bismuth using the electric field effect. The screening of
electron-electron interaction was found to increase with electron concentration
in a manner correlated with the tendency towards superconductivity. This does
not preclude an increase in the density of states being important in the
development of superconductivity. The superconductor-insulator transition
appears to belong to the universality class of the three dimensional XY model.Comment: Four pages, three figures. Revised slightly to reflect referees'
comment
Introduction: Urban revolutions in the age of global urbanism
This special issue, papers presented at an Urban Studies Foundation-funded conference in Jakarta (March 2011), examines the current ‘urban century’ in terms of three revolutions. Revolutions from above index the logics and norms of mainstream global urbanism, particularly the form they have taken as policymakers work with municipal officials worldwide to organise urban development around neoliberal norms. Revolutions from below refer to the multifaceted contestations of global urbanism that take place in and around cities, ranging from urban street demonstrations and occupations (such as those riveting the world in early 2011 when these papers were written) to the quotidian actions of those pursuing politics and livelihoods that subvert the norms of mainstream global urbanism. It also highlights conceptual revolutions, referencing the ongoing challenge of reconceptualising urban theory from the South – not simply as a hemispheric location or geopolitical category but an epistemological stance, staged from many different locations but always fraught with the differentials of power and the weight of historical geographies. Drawing on the insights of scholars writing from, and not just about, such locations, a further iteration in this ‘southern’ turn of urban theorising is proposed. This spatio-temporal conjunctural approach emphasises how the specificity of cities – their existence as entities that are at once singular and universal – emerges from spatio-temporal dynamics, connectivities and horizontal and vertical relations. Practically, such scholarship entails taking the field seriously through collaborative work that is multi-sited, engages people along the spectrum of academics and activists, and is presented before and scrutinised by multiple publics
Healthcare Reform in Latino Rhode Island: Perspectives of Spanish speakers and Insurance Navigators
Latinos have the highest uninsurance rates of any ethnic or racial group in the US despite recent health insurance expansion reform. In addition to immigration and language barriers, health literacy and attitudes may impact coverage disparities. Focus groups with Spanish-speaking community members and semi-structured interviews with health insurance navigators were conducted to explore knowledge, awareness, and attitudes towards healthcare reform among Latinos in Rhode Island. Sessions were audio recorded, transcribed, and analyzed employing standard qualitative methods. Thirty-two focus group participants and six navigators were enrolled in the study. Spanish-speaking participants demonstrated limited knowledge of the cost implications of the Medicaid Expansion and of the role of health insurance exchanges. Common misconceptions included that insurance costs would increase regardless of income, that enrollment would compromise green card and citizenship applications, that documented non-permanent residents would be ineligible for subsidies, and that reform benefits would apply to undocumented workers. Our findings suggest that local initiatives and providers should target Latinos in a culturally sensitive manner to increase literacy regarding insurance eligibility, affordability, points of access as well as to address misconceptions related to insurance eligibility for documented immigrants
Characterizing the Hofstadter butterfly's outline with Chern numbers
In this work, we report original properties inherent to independent particles
subjected to a magnetic field by emphasizing the existence of regular
structures in the energy spectrum's outline. We show that this fractal curve,
the well-known Hofstadter butterfly's outline, is associated to a specific
sequence of Chern numbers that correspond to the quantized transverse
conductivity. Indeed the topological invariant that characterizes the
fundamental energy band depicts successive stairways as the magnetic flux
varies. Moreover each stairway is shown to be labeled by another Chern number
which measures the charge transported under displacement of the periodic
potential. We put forward the universal character of these properties by
comparing the results obtained for the square and the honeycomb geometries.Comment: Accepted for publication in J. Phys. B (Jan 2009
Low-Temperature Glassy Response of Ultrathin Manganite Films to Electric and Magnetic Fields
The glassy response of thin films of La0.8Ca0.2MnO3 to external magnetic and
gated electrostatic fields in a field-effect geometry has been studied at low
temperatures. A hierarchical response with irreversible memory effects,
non-ergodic time evolution, aging and annealing behavior of the resistance
suggest that the dynamics are governed by strain relaxation for both electronic
and magnetic perturbations. Cross-coupling of charge, spin, and strain have
been exploited to tune the coercivity of an ultrathin manganite film by
electrostatic gating.Comment: 4 pages, 5 figure
Analytic Coulomb matrix elements in the lowest Landau level in disk geometry
Using Darling's theorem on products of generalized hypergeometric series an
analytic expression is obtained for the Coulomb matrix elements in the lowest
Landau level in the representation of angular momentum. The result is important
in the studies of Fractional Quantum Hall effect (FQHE) in disk geometry.
Matrix elements are expressed as simple finite sums of positive terms,
eliminating the need to approximate these quantities with slowly-convergent
series. As a by-product, an analytic representation for certain integals of
products of Laguerre polynomials is obtained.Comment: Accepted to J. Math. Phys.; 3 pages revtex, no figure
Color Magnetic Corrections to Quark Model Valence Distributions
We calculate order color magnetic corrections to the valence quark
distributions of the proton using the Los Alamos Model Potential wavefunctions.
The spin-spin interaction breaks the model SU(4) symmetry, providing a natural
mechanism for the difference between the up and down distributions. For a value
of sufficient to produce the mass splitting, we find up
and down quark distributions in reasonable agreement with experiment.Comment: 25 Pages, LA-UR-93-132
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