Advanced vehicle separation apparatus

A method of obtaining test data from two independent models or bodies in a conventional wind tunnel is described. The system makes efficient use of wind tunnel test time with computer control performing complex coordinate transformations necessary for model positioning. The apparatus is designed to be used in any of the three Unitary Wind Tunnels at NASA-Ames Research Center. Mechanical design details and a brief description of the control system for the separation apparatus are presented

Rotary mechanism for wind tunnel stall/spin studies

The critical problem of stall-spin characteristics of high performance aircraft and the need for experimental data in this area are reviewed. A rotary mechanism for obtaining this aerodynamic data in a conventional wind tunnel is presented. The intricacies of the drive systems and the articulation available through such a mechanism are described

The Pauli Equation for Probability Distributions

The "marginal" distributions for measurable coordinate and spin projection is introduced. Then, the analog of the Pauli equation for spin-1/2 particle is obtained for such probability distributions instead of the usual wave functions. That allows a classical-like approach to quantum mechanics. Some illuminating examples are presented.Comment: 14 pages, ReVTe

Bosonic sector of the two-dimensional Hubbard model studied within a two-pole approximation

The charge and spin dynamics of the two-dimensional Hubbard model in the paramagnetic phase is first studied by means of the two-pole approximation within the framework of the Composite Operator Method. The fully self-consistent scheme requires: no decoupling, the fulfillment of both Pauli principle and hydrodynamics constraints, the simultaneous solution of fermionic and bosonic sectors and a very rich momentum dependence of the response functions. The temperature and momentum dependencies, as well as the dependency on the Coulomb repulsion strength and the filling, of the calculated charge and spin susceptibilities and correlation functions are in very good agreement with the numerical calculations present in the literature

Electron-radiation interaction in a Penning trap: beyond the dipole approximation

We investigate the physics of a single trapped electron interacting with a radiation field without the dipole approximation. This gives new physical insights in the so-called geonium theory.Comment: 12 pages, RevTeX, 6 figures, Approved for publication in Phys. Rev.

A Study of the Antiferromagnetic Phase in the Hubbard Model by means of the Composite Operator Method

We have investigated the antiferromagnetic phase of the 2D, the 3D and the extended Hubbard models on a bipartite cubic lattice by means of the Composite Operator Method within a two-pole approximation. This approach yields a fully self-consistent treatment of the antiferromagnetic state that respects the symmetry properties of both the model and the algebra. The complete phase diagram, as regards the antiferromagnetic and the paramagnetic phases, has been drawn. We firstly reported, within a pole approximation, three kinds of transitions at half-filling: Mott-Hubbard, Mott-Heisenberg and Heisenberg. We have also found a metal-insulator transition, driven by doping, within the antiferromagnetic phase. This latter is restricted to a very small region near half filling and has, in contrast to what has been found by similar approaches, a finite critical Coulomb interaction as lower bound at half filling. Finally, it is worth noting that our antiferromagnetic gap has two independent components: one due to the antiferromagnetic correlations and another coming from the Mott-Hubbard mechanism.Comment: 20 pages, 37 figures, RevTeX, submitted to Phys. Rev.

Modelling Post-tensioned Precast Concrete Segmental Girder Bridges with Keyed Joints – Preliminary Results

Precast concrete segmental bridges (PCSBs) have been the most common design technology used in the last decades. It is widely recognized that segmental bridges have better durability, lower life-cycle costs and higher quality for maintenance than other types of bridges. PCSBs with externally prestressed tendons have become very popular in construction because of economical and safety reasons, fast and practical construction, and outstanding serviceability. Moreover, external tendons technique is widely used because it allows to inspect the cables and to replace them or to reinforce the tendons in case of damage while such kinds of actions are difficult to be taken in case of internal prestressing. Therefore, box section is the most common solution due to its aesthetic appeal and elegance that reduces the environmental impact as well due to the convenient maintenance for the tendons. Besides, the hollow concrete box segment can be used for service/electrical cable ducts for bridges. However, there is lack of reliable computational model for analysing behaviour of post-tensioned PCSBs. This research investigates the behaviour of PCSBs with dry keyed joints and external tendons up to failure with the use of finite element method which is validated by comparing experimental results. Deflection, joint opening, tendon slip, stresses of the tendons and the concrete are obtained from numerical analysis with recommendation on further development towards a more accurate numerical model for PCSBs made

Koagulacija krvi i lipidi u serumu (Studija stanovništva)

Two population groups differing in dietary habits and physical activity were examined on blood lipids and blood coagulability. The results showed a higher lipid concentration and shorter clotting time in the physically less active group, having a higher fat and caloric intake.Dvije populacione grupe, koje se razlikuju po svojoj prehrani, a osobito po povećanoj potrošnji masnoća i smanjenom fizičkom aktivitetu, ispitivane su s obzirom na nivo krvnih lipida i na koagulabilitet krvi. Rezultati pokazuju, da prehrana, osobito povećana potrošnja animalnih masnoća, te smanjena psihička aktivnost utječu na povećanje nivoa krvnih lipida i bržeg koagulabiliteta krvi mjerenog kao vrijeme zgrušavanja i protrombinsko vrijeme. Ti rezultati potvrđuju već ranija zapažanja autora o povećanom koagulabilitetu krvi u populacionim grupama, koje se istovremeno razlikuju i u koncentraciji krvnih lipida i u učestalosti koronarnih bolesti

Continuous quantum nondemolition feedback and unconditional atomic spin squeezing

We discuss the theory and experimental considerations of a quantum feedback scheme for producing deterministically reproducible spin squeezing. Continuous nondemolition atom number measurement from monitoring a probe field conditionally squeezes the sample. Simultaneous feedback of the measurement results controls the quantum state such that the squeezing becomes unconditional. We find that for very strong cavity coupling and a limited number of atoms, the theoretical squeezing approaches the Heisenberg limit. Strong squeezing will still be produced at weaker coupling and even in free space (thus presenting a simple experimental test for quantum feedback). The measurement and feedback can be stopped at any time, thereby freezing the sample with a desired amount of squeezing.Comment: 17 pages, 5 figures, submitted to JP