New concept in brazing metallic honeycomb panels

Aluminum oxide coating provides surface which will not be wetted by brazing alloy and which stops metallic diffusion welding of tooling materials to part being produced. This method eliminates loss of tooling materials and parts from braze wetting and allows fall-apart disassembly of tooling after brazing

Dynamics of a liquid dielectric attracted by a cylindrical capacitor

The dynamics of a liquid dielectric attracted by a vertical cylindrical capacitor is studied. Contrary to what might be expected from the standard calculation of the force exerted by the capacitor, the motion of the dielectric is different depending on whether the charge or the voltage of the capacitor is held constant. The problem turns out to be an unconventional example of dynamics of a system with variable mass, whose velocity can, in certain circumstances, suffer abrupt changes. Under the hypothesis that the voltage remains constant the motion is described in qualitative and quantitative details, and a very brief qualitative discussion is made of the constant charge case.Comment: To appear in European Journal of Physic

Force on a neutral atom near conducting microstructures

We derive the non-retarded energy shift of a neutral atom for two different geometries. For an atom close to a cylindrical wire we find an integral representation for the energy shift, give asymptotic expressions, and interpolate numerically. For an atom close to a semi-infinite halfplane we determine the exact Green's function of the Laplace equation and use it derive the exact energy shift for an arbitrary position of the atom. These results can be used to estimate the energy shift of an atom close to etched microstructures that protrude from substrates.Comment: 7 pages, 5 figure

On the exact electric and magnetic fields of an electric dipole

We derive from Jefimenko's equations a multipole expansion in order to obtain the exact expressions for the electric and magnetic fields of an electric dipole with an arbitrary time dependence. A few comments are also made about the usual expositions found in most common undergraduate and graduate textbooks as well as in the literature on this topic

Theory of Tunneling for Rough Junctions

A formally exact expression for the tunneling current, for its separation into specular and diffuse components, and for its directionality, is given for a thick tunnel junction with rough interfaces in terms of the properties of appropriately defined scattering amplitudes. An approximate evaluation yields the relative magnitudes of the specular and diffuse components, and the angular dependence of the diffuse component, in terms of certain statistical properties of the junction interfaces.Comment: 4 page

Unified description of ballistic and diffusive carrier transport in semiconductor structures

A unified theoretical description of ballistic and diffusive carrier transport in parallel-plane semiconductor structures is developed within the semiclassical model. The approach is based on the introduction of a thermo-ballistic current consisting of carriers which move ballistically in the electric field provided by the band edge potential, and are thermalized at certain randomly distributed equilibration points by coupling to the background of impurity atoms and carriers in equilibrium. The sum of the thermo-ballistic and background currents is conserved, and is identified with the physical current. The current-voltage characteristic for nondegenerate systems and the zero-bias conductance for degenerate systems are expressed in terms of a reduced resistance. For arbitrary mean free path and arbitrary shape of the band edge potential profile, this quantity is determined from the solution of an integral equation, which also provides the quasi-Fermi level and the thermo-ballistic current. To illustrate the formalism, a number of simple examples are considered explicitly. The present work is compared with previous attempts towards a unified description of ballistic and diffusive transport.Comment: 23 pages, 10 figures, REVTEX

The impact of long-term soccer-specific training on the physical development of elite junior soccer players

The goal of any soccer talent development programme is to guide players towards professional characteristics. In order to maximise this process it is essential to gain an insight into their individual characteristics. Within this specific population there are many factors from maturation, hormonal, anatomical and musculoskeletal changes that accompany paediatric development and consequently have a direct impact upon their development. The aim of this thesis was to determine the relative influence of changes in maturation and long-term systematic training on the physical development of elite junior soccer players. The aim of the first study (Chapter 4) was to assess the reliability of a range of anthropometric and performance measures in aged matched academy and non-academy soccer players (U14-18). The results demonstrated that all anthropometric (%CV values of 0.1 – 1.3%) and performance measures (%CV values of 1.8-6.2%) were highly reproducible in both the academy and non-academy soccer players. These assessments would be subsequently used to determine the impact of long-term training on changes in physical development of junior soccer players. The aim of study two (Chapter 5) was to determine the validity of a non-invasive approach (maturity offset) for predicting end height stature in academy soccer players (U14-18). Overall, agreement between estimates of end height stature in elite youth soccer players’ using skeletal x-ray and the maturity-offset method were poor with a SEM and 95 % LOA of 4 cm and +11cm being observed respectively. These findings indicate that care must be taken when predicating end height stature in academy soccer players when using maturity offset method. The aim of the third study (Chapter 6) was to examine the typical weekly training load experienced by academy and non-academy soccer players (U12-U16) during the in-season competitive period. Physiological loading associated with training sessions and match-play were monitored using heart rate (HR) and ratings of perceived exertion (RPE). Training and match loads were calculated by multiplying global session RPE and duration (RPE-TL). Weekly training load in the academy players (U12, 737±51; U14, 646±106; U16, 750±81) was higher than the non-academy players (U12, 157±28; U14, 161±19; U16, 193±26) across the three age groups. Similarly, match load and % time spent >90%HRmax was higher in the academy players compared to the non-academy players. The present findings indicate that the overall load and intensity of training is greater in academy players compared to aged match non-academy players. The aim of the fourth study (Chapter 7) was to determine the relative influence of changes in maturation and long-term systematic training on changes in physical performance in age matched academy and non-academy junior soccer player. The three-year change in the physical performance of twenty-seven academy and eighteen non-academy soccer players (U12-U16) were monitored. When corrected for differences in both baseline performance and change in maturity status (maturity offset), greater changes in countermovement jump (7.3 + 2.6 cm, 5.4 + 2.5 cm), 10 m (-0.15 + 0.05 s, -0.10 + 0.04 s) and 20 m sprint (-0.30 + 0.16 s, -0.15 + 0.13 s), agility (-0.19 + 0.01 s, -0.08 + 0.08 s), repeated sprint (-0.60 + 0.26 s, -0.41 + 2.1 s) and intermittent endurance capacity (1128 + 406 m, 315 + 370 m) were observed in the Academy players compared with non-academy players (p0.7). These findings indicate that long-term player development programs accelerate the rate physical development of academy soccer players relative to age and maturity matched non-academy players. In summary, the present thesis highlights that academy soccer players experience greater rates of improvement in physical performance indicators compared to non-academy players, independently from the initial performance level of the child and change in maturation over the same time period. These difference are likely to reflect the increased volume and intensity of soccer-specific training experienced by the young soccer players as part of the academy’s approach to long-term athlete development. Future research is warranted in order to determine training loads in elite youth soccer players at different stages of biological maturity which serve to enhance performance whilst minimising the risk of injury

Brillouin-Wigner perturbation theory in open electromagnetic systems

A Brillouin-Wigner perturbation theory is developed for open electromagnetic systems which are characterised by discrete resonant states with complex eigenenergies. Since these states are exponentially growing at large distances, a modified normalisation is introduced that allows a simple spectral representation of the Green's function. The perturbed modes are found by solving a linear eigenvalue problem in matrix form. The method is illustrated on exactly solvable one- and three-dimensional examples being, respectively, a dielectric slab and a microsphere.Comment: 6 pages, 2 figure