146 research outputs found
A Pulse Shaping Algorithm of a Coherent Matter Wave. Controlling Reaction Dynamics
A pulse shaping algorithm for a matter wave with the purpose of controlling a
binary reaction has been designed. The scheme is illustrated for an Eley-Rideal
reaction where an impinging matter-wave atom recombines with an adsorbed atom
on a metal surface. The wave function of the impinging atom is shaped such that
the desorbing molecule leaves the surface in a specific vibrational state.Comment: 4 pages, 5 figure
EFFECTS OF SHORT-TERM SLED TOWING AND UNLOADED SPRINT TRAINING ON LEG POWER AND STIFFNESS
The relationship between stiffness and athletic performance is of great interest to the sport and research communities. Unfortunately, there are no longitudinal studies that have investigated the effects of strength or power training on mechanical stiffness in sprinters. The aim of the study was to examine the effect of resisted and unloaded sprint training programs on sprint time, leg power, and stiffness
Classical emulation of quantum-coherent thermal machines
The performance enhancements observed in various models of continuous quantum
thermal machines have been linked to the buildup of coherences in a preferred
basis. But, is this connection always an evidence of `quantum-thermodynamic
supremacy'? By force of example, we show that this is not the case. In
particular, we compare a power-driven three-level continuous quantum
refrigerator with a four-level combined cycle, partly driven by power and
partly by heat. We focus on the weak driving regime and find the four-level
model to be superior since it can operate in parameter regimes in which the
three-level model cannot, it may exhibit a larger cooling rate, and,
simultaneously, a better coefficient of performance. Furthermore, we find that
the improvement in the cooling rate matches the increase in the stationary
quantum coherences exactly. Crucially, though, we also show that the
thermodynamic variables for both models follow from a classical representation
based on graph theory. This implies that we can build incoherent
stochastic-thermodynamic models with the same steady-state operation or,
equivalently, that both coherent refrigerators can be emulated classically.
More generally, we prove this for any N-level weakly driven device with a
`cyclic' pattern of transitions. Therefore, even if coherence is present in a
specific quantum thermal machine, it is often not essential to replicate the
underlying energy conversion process.Comment: 13 pages, 4 figures; references updated; appendix adde
EFFECTS OF UPHILL RUNNING ON SPRINTING TECHNIQUE IN FOOTBALL PLAYERS
The success in many actions in team sports is determined by the player’s ability to develop high speed and acceleration. There are many resisted methods for training the strength within the specific running technique, each one with different application according to the characteristics of the overload. Uphill sprinting is one of these methods. A criticism related to the use of resisted methods is that the athletes may use a modified running technique and so subsequently could alter their movement pattern if repeated in time (e.g. Alcaraz et al. (2008) showed that some methods modify the body lean). The purpose of this work was to clarify the effects of uphill sprinting on variables related to the running performance and technique in football players
Stabilization of Ultracold Molecules Using Optimal Control Theory
In recent experiments on ultracold matter, molecules have been produced from
ultracold atoms by photoassociation, Feshbach resonances, and three-body
recombination. The created molecules are translationally cold, but
vibrationally highly excited. This will eventually lead them to be lost from
the trap due to collisions. We propose shaped laser pulses to transfer these
highly excited molecules to their ground vibrational level. Optimal control
theory is employed to find the light field that will carry out this task with
minimum intensity. We present results for the sodium dimer. The final target
can be reached to within 99% if the initial guess field is physically
motivated. We find that the optimal fields contain the transition frequencies
required by a good Franck-Condon pumping scheme. The analysis is able to
identify the ranges of intensity and pulse duration which are able to achieve
this task before other competing process take place. Such a scheme could
produce stable ultracold molecular samples or even stable molecular
Bose-Einstein condensates
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