SU(3) Thermodynamics on Small Lattices

The free energy density of the SU(3) gauge theory at temperatures T/T_c = 4/3, 3/2 and 2 is calculated on lattices with temporal extent as small as N_t = 2, 3 and spatial extent N_s = 4 N_t using parametrized fixed point actions. Although cut-off effects are seen, they are hugely suppressed with respect to Wilson and Symanzik-improved actions and at N_t = 3 there is already a good agreement with the continuum limit as extrapolated from the results with the Wilson action at N_t = 6 and 8.Comment: 19 pages (latex text + 6 eps figures) in a uuencoded compressed tar fil

One-loop Reggeon-Reggeon-gluon vertex at arbitrary space-time dimension

In order to check the compatibility of the gluon Reggeization in QCD with the $s$-channel unitarity, the one-loop correction to the Reggeon-Reggeon-gluon vertex must be known at arbitrary space-time dimension $D$. We obtain this correction from the gluon production amplitude in the multi-Regge kinematics and present an explicit expression for it in terms of a few integrals over the transverse momenta of virtual particles. The one-gluon contribution to the non-forward BFKL kernel at arbitrary $D$ is also obtained.Comment: 22 pages, LaTe

Constrained Molecular Dynamics II: a N-body approach to nuclear systems

In this work we illustrate the basic development of the constrained molecular dynamics applied to the N-body problem in nuclear physics. The heavy computational taskes related to quantum effects, to the presence of the "hard core" repulsive interaction have been worked out by defining a set of transformations based on the concept of impulsive forces. In particular in the implemented version II of the Constrained Molecular Dynamics model the problem related to the non conservation of the total angular momentum has been solved. This problem can affect others semiclassical microscopic approaches as due to the "hard core" repulsive interaction or to the use of stochastic forces. The effect of the restored conservation law on the fusion cross section for 40Ca+40Ca system is also briefly discussed.Comment: Tex version 3.1459 (Web2C 7.3.1);main text+fig.cap in .tex 13 page; +4 figures .ps;the order and the numerical label of the figure files reflect the figure numbers in the main tex and captions, Submited to Journal of computational physic

Real-time extraction of growth rates from rotating substrates during molecular-beam epitaxy

We present a method for measuring molecular‐beam epitaxy growth rates in near real‐time on rotating substrates. This is done by digitizing a video image of the reflection high‐energy electron diffraction screen, automatically tracking and measuring the specular spot width, and using numerical techniques to filter the resulting signal. The digitization and image and signal processing take approximately 0.4 s to accomplish, so this technique offers the molecular‐beam epitaxy grower the ability to actively adjust growth times in order to deposit a desired layer thickness. The measurement has a demonstrated precision of approximately 2%, which is sufficient to allow active control of epilayer thickness by counting monolayers as they are deposited. When postgrowth techniques, such as frequency domain analysis, are also used, the reflection high‐energy electron diffraction measurement of layer thickness on rotating substrates improves to a precision of better than 1%. Since all of the components in the system described are commercially available, duplication is straightforward

'Moving to Access' in Transport Planning: Identifying Barriers, Designing Strategies

Accessibility is a well-established concept in planning research. It measures the ease of reaching destinations or activities, or the potential for interaction (Hansen, 1959). In very general terms, accessibility can be defined as the level of ability to successfully reach a certain object, place, event, or person. It is a key concept for understanding the social and economic life of cities in particular and societies in general. The purpose of this paper is to inform the ‘accessibility approach’ to transport policy, planning, and investment by means of critically analysing its implementation barriers in professional circles and how to overcome them. We argue that it is necessary to focus less on technological issues such as what are the best instruments and decision-making tools to promote the accessibility approach. There is now sufficient knowledge about that (Papa et al. 2016). Now, the priority is to identify the institutional, organisational and cultural barriers to this approach. Mobility and transport networks can facilitate accessibility, but only to a certain extent. Defining accessibility as what is granted by mobility is a reductionism. In our view, mobility is in many cases a necessary condition for accessibility, but rarely is a sufficient one. Traditional transport planning has in numerous instances failed to realise this important nuance. As a result, traditional transport planning has frequently equated implementing measures aimed at increasing mobility to improvements in accessibility levels. That is not necessarily a very accurate way of understanding what happens. This is fully acknowledged by the accessibility planning approach. In fact, accessibility planning recognises that the absolute opposite to that might be closer to the truth: increasing mobility might represent less accessibility (Ferreira and Batey, 2007). Conflicts between accessibility planning and the dominant transport planning culture have been a barrier to effective implementation of accessibility planning (Bertolini et al. 2005; Bertolini, 2012). This approach of ‘mobility-first’ planning and investment has largely failed to deliver on the broader urban goals relating to economic growth, social integration, and sustainable development. Conversely, implementing accessibility-based performance measures can allow regions to pursue more coordinated objectives around economic opportunity, social equity, well-being, and health. Several reasons should encourage the application of the accessibility planning approach., as the potential benefits of using the accessibility approach in applied planning practice are massive. Among other benefits, it facilitates understanding with much greater accuracy how different social groups are served in different ways by the transport system and by public and private services. It also facilitates identifying with higher precision what prevents people from reaching certain places and develop or maintain certain connections. This happens because it offers valuable insights on matters as diverse as mobility and transport, time budgets and schedules, nature and quality of services, financial and economic constraints, just to mention some possibilities. For further insights see, for example, Ferreira and Batey (2007). Another reason is that the accessibility approach has the potential of bringing diverse activity sectors (e.g. transport and land use, economics and health care, education and logistics) together to agree on shared actions. This happens because the accessibility approach makes evident the interconnections between individual preferences and characteristics, geodemographic properties, nature and quality of services available, and mobility issues such as travel time savings, travel costs, and levels of service experienced in the transport network. This is not the case with the traditional transport planning approach as its focus is narrower and essentially concerned with mobility issues. A benefit is also that the accessibility approach has the potential to create a common language among different stakeholders for discussing community conditions and priorities. In this way this approach offers a particularly constructive framework for action on agendas shared by transport authorities, citizens, service providers, technical experts, and land owners. It is also very constructive for creating communication bridges among people with different academic and technical backgrounds. This happens because its epistemological underpinnings are strongly linked with social inclusion theory and its theoretical basis is not mathematics, economics or engineering (which tend to be quite exclusive disciplinary areas), but social science in general and planning in particular. Finally, another advantage is that the accessibility approach is abundantly equipped with appealing visualisation tools and techniques capable of depicting information in very clear ways. It can therefore facilitate decision-making processes by means of providing powerful visual inputs that integrate and give answers to a wide range of questions and policy issues. However, a number of barriers exist to making the use of the accessibility approach mainstream. As a result, mobility-oriented planning continues to dominate the professional world. In this paper we aim at uncovering the barriers that planners face when trying to apply the accessibility approach in planning practice and on the pathways to overcome these barriers. This research aim is relevant and timely. Indeed, in the existing literature the main focus has been on the technical properties of accessibility measures and tools, with some exceptions (Curtis & Low, 2012; Geurs & Halden, 2015; Halden, 2014). We believe that accessibility planning research needs now to move on to study in greater detail the institutional barriers that prevent the implementation of the accessibility approach. There are strong reasons to believe that stakeholders involved in planning processes are prone to perceive the accessibility planning approach as something with massive potential, but only when this is introduced in the right institution, adopting the best approach, with the appropriate strategic support, for the appropriate goals, with the correct indicators and datasets, and with the correct timing. The paper is structured as follows. Following this introduction, section 2 provides a brief description of the methodology used. Section 3 reports the results of the expert’s survey, discussing the barriers to the implementation of the accessibility approach in planning practice and discusses pathways to mainstream accessibility planning. Some concluding remarks are drawn in section 4

Mass gap in the 2D O(3) non-linear sigma model with a theta=pi term

By analytic continuation to real theta of data obtained from numerical simulation at imaginary theta we study the Haldane conjecture and show that the O(3) non-linear sigma model with a theta term in 2 dimensions becomes massless at theta=3.10(5). A modified cluster algorithm has been introduced to simulate the model with imaginary theta. Two different definitions of the topological charge on the lattice have been used; one of them needs renormalization to match the continuum operator. Our work also offers a successful test for numerical methods based on analytic continuation.Comment: Latex file, 4 pages. To appear in PRD; it contains the justification of analicity, more details about the fits, more references, et