3,269 research outputs found
Cutting temperature measurement and material machinability
Cutting temperature is very important parameter of cutting process. Around
90% of heat generated during cutting process is then away by sawdust, and the
rest is transferred to the tool and workpiece. In this research cutting
temperature was measured with artificial thermocouples and question of
investigation of metal machinability from aspect of cutting temperature was
analyzed. For investigation of material machinability during turning
artificial thermocouple was placed just below the cutting top of insert, and
for drilling thermocouples were placed through screw holes on the face
surface. In this way was obtained simple, reliable, economic and accurate
method for investigation of cutting machinability
A Dataflow Graphical Language for Database Applications
In this paper we discuss a graphical language for information retrieval and processing. A lot of recent activity has occurred in the area of improving access to database systems. However, current results are restricted to simple interfacing of database systems. We propose a graphical language for specifying complex applications
Phase Conjugation and Negative Refraction Using Nonlinear Active Metamaterials
We present experimental demonstration of phase conjugation using nonlinear
metamaterial elements. Active split-ring resonators loaded with varactor diodes
are demonstrated theoretically to act as phase-conjugating or time-reversing
discrete elements when parametrically pumped and illuminated with appropriate
frequencies. The metamaterial elements were fabricated and shown experimentally
to produce a time reversed signal. Measurements confirm that a discrete array
of phase-conjugating elements act as a negatively-refracting time reversal RF
lens only 0.12 thick
Lieb-Thirring Bound for Schr\"odinger Operators with Bernstein Functions of the Laplacian
A Lieb-Thirring bound for Schr\"odinger operators with Bernstein functions of
the Laplacian is shown by functional integration techniques. Several specific
cases are discussed in detail.Comment: We revised the first versio
Shock waves in ultracold Fermi (Tonks) gases
It is shown that a broad density perturbation in a Fermi (Tonks) cloud takes
a shock wave form in the course of time evolution. A very accurate analytical
description of shock formation is provided. A simple experimental setup for the
observation of shocks is discussed.Comment: approx. 4 pages&figures, minor corrections^2, to be published as a
Letter in Journal of Physics
Formation of shock waves in a Bose-Einstein condensate
We consider propagation of density wave packets in a Bose-Einstein
condensate. We show that the shape of initially broad, laser-induced, density
perturbation changes in the course of free time evolution so that a shock wave
front finally forms. Our results are well beyond predictions of commonly used
zero-amplitude approach, so they can be useful in extraction of a speed of
sound from experimental data. We discuss a simple experimental setup for shock
propagation and point out possible limitations of the mean-field approach for
description of shock phenomena in a BEC.Comment: 8 pages & 6 figures, minor changes, more references, to appear in
Phys. Rev.
How to fix a broken symmetry: Quantum dynamics of symmetry restoration in a ferromagnetic Bose-Einstein condensate
We discuss the dynamics of a quantum phase transition in a spin-1
Bose-Einstein condensate when it is driven from the magnetized
broken-symmetry phase to the unmagnetized ``symmetric'' polar phase. We
determine where the condensate goes out of equilibrium as it approaches the
critical point, and compute the condensate magnetization at the critical point.
This is done within a quantum Kibble-Zurek scheme traditionally employed in the
context of symmetry-breaking quantum phase transitions. Then we study the
influence of the nonequilibrium dynamics near a critical point on the
condensate magnetization. In particular, when the quench stops at the critical
point, nonlinear oscillations of magnetization occur. They are characterized by
a period and an amplitude that are inversely proportional. If we keep driving
the condensate far away from the critical point through the unmagnetized
``symmetric'' polar phase, the amplitude of magnetization oscillations slowly
decreases reaching a non-zero asymptotic value. That process is described by
the equation that can be mapped onto the classical mechanical problem of a
particle moving under the influence of harmonic and ``anti-friction'' forces
whose interplay leads to surprisingly simple fixed-amplitude oscillations. We
obtain several scaling results relating the condensate magnetization to the
quench rate, and verify numerically all analytical predictions.Comment: 15 pages, 11 figures, final version accepted in NJP (slight changes
with respect to the former submission
- …