373 research outputs found
Passive motion control of pneumatically driven displacers in cryogenic coolers
The split cryogenic cooler with a remote cold finger offers many advantages for use in cooling of infrared systems. A pneumatic drive for the displacer in such coolers was adopted in many cryocooler designs. This concept can be significantly improved by causing the displacer to move sinusoidally rather than in an essentially square wave, as in most of the present models. The way this motion was achieved passively is described and its advantages outlined. Data of minicoolers using this concept are presented
Magnetic trapping of neutral particles: Classical and Quantum-mechanical study of a Ioffe-Pritchard type trap
Recently, we developed a method for calculating the lifetime of a particle
inside a magnetic trap with respect to spin flips, as a first step in our
efforts to understand the quantum-mechanics of magnetic traps. The 1D toy model
that was used in this study was physically unrealistic because the magnetic
field was not curl-free. Here, we study, both classically and
quantum-mechanically, the problem of a neutral particle with spin S, mass m and
magnetic moment mu, moving in 3D in an inhomogeneous magnetic field
corresponding to traps of the Ioffe-Pritchard, `clover-leaf' and `baseball'
type. Defining by omega_p, omega_z and omega_r the precessional, the axial and
the lateral vibrational frequencies, respectively, of the particle in the
adiabatic potential, we find classically the region in the $(\omega_{r}%
(omega_r -- omega_z) plane where the particle is trapped.
Quantum-mechanically, we study the problem of a spin-one particle in the same
field. Treating omega_r / omega_p and omega_z / omega_p as small parameters for
the perturbation from the adiabatic Hamiltonian, we derive a closed-form
expression for the transition rate 1/T_{esc} of the particle from its trapped
ground-state. We find that in the extreme cases, the expression for 1/T_{esc}
is dominated by the largest of the two frequencies omega_r and omega_z.Comment: 25 pages + 1 EPS figur
Universal lineshape of the Kondo zero-bias anomaly in a quantum dot
Encouraged by the recent real-time renormalization group results we carried
out a detailed analysis of the nonequilibrium Kondo conductance observed in an
InAs nanowire-based quantum dot and found them to be in excellent agreement. We
show that in a wide range of bias the Kondo conductance zero-bias anomaly is
scaled by the Kondo temperature to a universal lineshape predicted by the
numerical study. The lineshape can be approximated by a phenomenological
expression of a single argument . The knowledge of
an analytical expression for the lineshape provides an alternative way for
estimation of the Kondo temperature in a real experiment, with no need for time
consuming temperature dependence measurements of the linear conductance.Comment: 5 pages, 3 figure
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