Preasymptotic nature of hadron scattering vs small-x HERA Data

We emphasize that recently observed regularities in hadron interactions and deep-inelastic scattering are of preasymptotic nature and it is impossible to make conclusions on the true asymptotic behavior of observables without unitarization procedure. Unitarization is important and changes scattering picture drastically.Comment: LaTeX file, 9 pages; 4 tarred, gzipped and uuencoded figures in a separate fil

Effective String Theory of Vortices and Regge Trajectories

Starting from a field theory containing classical vortex solutions, we obtain an effective string theory of these vortices as a path integral over the two transverse degrees of freedom of the string. We carry out a semiclassical expansion of this effective theory, and use it to obtain corrections to Regge trajectories due to string fluctuations.Comment: 27 pages, revtex, 3 figures, corrected an error with the cutoff in appendix E (was previously D), added more discussion of Fig. 3, moved some material in section 9 to a new appendi

Two-Dimensional Self-Assembly in Diblock Copolymers

Submitted to Phys. Rev. Lett.Diblock copolymers confined to a two-dimensional surface may produce uniform features of macromolecular dimensions (10 â 100 nm). We present a mathematical model for nanoscale pattern formation in such polymers which captures the dynamic evolution of a solution of poly(styrene)- b-poly(ethylene oxide), PS-b-PEO, in solvent at an air-water interface. The model has no fitting parameters and incorporates the effects of surface tension gradients, entanglement or vitrification, and diffusion. The resultant morphologies are quantitatively compared with experimental data.NS

The high temperature expansion of the classical XYZXYZ chain

We present the $\beta$-expansion of the Helmholtz free energy of the classical $XYZ$ model, with a single-ion anisotropy term and in the presence of an external magnetic field, up to order $\beta^{12}$. We compare our results to the numerical solution of Joyce's [Phys. Rev. Lett. 19, 581 (1967)] expression for the thermodynamics of the $XXZ$ classical model, with neither single-ion anisotropy term nor external magnetic field. This comparison shows that the derived analytical expansion is valid for intermediate temperatures such as $kT/J_x \approx 0.5$. We show that the specific heat and magnetic susceptibility of the spin-2 antiferromagnetic chain can be approximated by their respective classical results, up to $kT/J \approx 0.8$, within an error of 2.5%. In the absence of an external magnetic field, the ferromagnetic and antiferromagnetic chains have the same classical Helmholtz free energy. We show how this two types of media react to the presence of an external magnetic field

Re-inventing the wheel for the next generation of planetary rovers

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 84-85).Experiences with Spirit and Opportunity, the twin Mars Exploration Rovers, showed that one of the major issues that needs to be addressed in order to expand the exploration capabilities of planetary rovers is that of wheel traction. The relationships governing how much traction a wheel can produce are highly dependent on both the shape of the wheel and terrain properties. These relationships are complex and not yet fully understood. The amount of power required to drive a wheel is also dependent on its shape and the terrain properties. Wheel sizes that tend to maximize traction also tend to require more power. In the past, it has always been a challenge to find the right balance between designing a rover wheel with high traction capabilities and low power requirements. More recently, researchers invented the idea of a reconfigurable wheel which would have the ability to change its shape to adapt to the type of terrain it was on. In challenging terrain environments, the wheel could configure to a size that would maximize traction. In less challenging terrain environments, the wheel could configure to a size that would minimize power. Theoretical simulation showed that the use of reconfigurable wheels could improve tractive performance and some initial prototyping and experimental testing corroborated those findings. The purpose of this project was to extend that prototyping and experimenting. Four reconfigurable wheels were designed, built, and integrated onto an actual rover platform. A control methodology whereby the wheels could autonomously reconfigure was also designed, implemented, and demonstrated. The rover was then tested in a simulated Martian environment to assess the effectiveness of the reconfigurable wheels. During the tests, the power consumption and the distance traveled by the rover were both measured and recorded. In all tests, the wheels were able to successfully reconfigure and the rover continued to advance forward; but as was expected, the reconfigurable wheel system consumed more power than a non-reconfigurable wheel system. In the end, the results showed that if maximizing vehicle traction was weighed more heavily than minimizing power consumption, the use of reconfigurable wheels yielded a net gain in performance.by Brittany Baker.S.M

Nucleation and growth of Pt atomic layer deposition on Al2O3 substrates using (methylcyclopentadienyl)-trimethyl platinum and O2 plasma

The nucleation and growth of Pt atomic layer deposition (ALD) on Al2O3 substrates was studied using (methylcyclopentadienyl)-trimethyl platinum (MeCpPtMe3) and O2 plasma as the reactants. The nucleation of Pt ALD was examined on Al2O3 ALD substrates at 300¿°C using a variety of techniques including spectroscopic ellipsometry, x-ray reflectivity, x-ray photoelectron spectroscopy, and scanning electron microscopy. These techniques revealed that Pt ALD does not nucleate and grow immediately on the Al2O3 ALD substrates. There was negligible Pt ALD during the first 38 ALD cycles. The Pt ALD growth rate then increased substantially during the next 12 ALD cycles. Subsequently, the Pt ALD growth rate reached a steady state linear growth regime for >50 ALD cycles. These measurements suggest that the Pt ALD first forms a number of nanoclusters that grow slowly during the first 38 ALD cycles. These islands then merge during the next 12 cycles and yield a steady state Pt ALD growth rate of ~0.05 nm/cycle for >50 ALD cycles. The Pt ALD film at the onset of the steady state linear growth regime was approximately 2–3 nm in thickness. However, the SEM images of these Pt ALD films appeared corrugated and wormlike. These films also had a density that was only 50–70% of bulk Pt. Film densities that were consistent with bulk Pt were not observed until after >100 ALD cycles when the Pt ALD films appeared much smoother and were 4–5 nm in thickness. The Pt ALD nucleation rate could be enhanced somewhat using different O2 plasma parameters

Approximate Homomorphisms of Ternary Semigroups

A mapping $f:(G_1,[ ]_1)\to (G_2,[ ]_2)$ between ternary semigroups will be called a ternary homomorphism if $f([xyz]_1)=[f(x)f(y)f(z)]_2$. In this paper, we prove the generalized Hyers--Ulam--Rassias stability of mappings of commutative semigroups into Banach spaces. In addition, we establish the superstability of ternary homomorphisms into Banach algebras endowed with multiplicative norms.Comment: 10 page

On quantum deformation of conformal symmetry: Gauge dependence via field redefinitions

The effective action in gauge theories is known to depend on a choice of gauge fixing conditions. This dependence is such that any change of gauge conditions is equivalent to a field redefinition in the effective action. In this sense, the quantum deformation of conformal symmetry in the N = 4 super Yang-Mills theory, which was computed in 't Hooft gauge in hep-th/9808039 and hep-th/0203236, is gauge dependent. The deformation is an intrinsic property of the theory in that it cannot be eliminated by a local choice of gauge (although we sketch a field redefinition induced by a nonlocal gauge which, on the Coulomb branch of the theory, converts the one-loop quantum-corrected conformal transformations to the classical ones). We explicitly compute the deformed conformal symmetry in R_\xi gauge. The conformal transformation law of the gauge field turns out to be \xi-independent. We construct the scalar field redefinition which relates the 't Hooft and R_\xi gauge results. A unique feature of 't Hooft gauge is that it makes it possible to consistently truncate the one-loop conformal deformation to the terms of first order in derivatives of the fields such that the corresponding transformations form a field realization of the conformal algebra.Comment: 14 pages, latex, no figures; references and comments added, the final version to appear in PL

The Strong CP Problem and Axions

I describe how the QCD vacuum structure, necessary to resolve the $U(1)_A$ problem, predicts the presence of a P, T and CP violating term proportional to the vacuum angle $\bar{\theta}$. To agree with experimental bounds, however, this parameter must be very small $(\bar{\theta} \leq 10^{-9}$). After briefly discussing some possible other solutions to this, so-called, strong CP problem, I concentrate on the chiral solution proposed by Peccei and Quinn which has associated with it a light pseudoscalar particle, the axion. I discuss in detail the properties and dynamics of axions, focusing particularly on invisible axion models where axions are very light, very weakly coupled and very long-lived. Astrophysical and cosmological bounds on invisible axions are also briefly touched upon.Comment: 14 pages, to appear in the Lecture Notes in Physics volume on Axions, (Springer Verlag

Factors Influencing Trust in Agencies That Disseminate Tobacco Prevention Information

Several health-related agencies administer national and targeted public education campaigns to provide health information and change health-related behaviors. The trust the public has in these agencies as the source of the message impacts the effectiveness of their communication campaigns. In this study, we explore the perceived trust of agencies that communicate health messages in the tobacco control field. As part of a larger tobacco regulatory science study, we conducted six 90-min focus groups comprising 41 participants. Five main themes emerged pertinent to the agency: (1) its integrity, (2) its competence, (3) its motives, (4) how it is portrayed in the media, and (5) skepticism and mistrust about it. Given the significant resources spent on health messaging to the public and potential benefits offered by this communication, an understanding of public trust in the agencies as the source of health messages is important. Findings suggest health information may be ignored or discounted when there is mistrust in the agency sending those messages