High-order harmonic generation from Rydberg states at fixed Keldysh parameter

Because the commonly adopted viewpoint that the Keldysh parameter $\gamma$ determines the dynamical regime in strong field physics has long been demonstrated to be misleading, one can ask what happens as relevant physical parameters, such as laser intensity and frequency, are varied while $\gamma$ is kept fixed. We present results from our one- and fully three-dimensional quantum simulations of high-order harmonic generation (HHG) from various bound states of hydrogen with $n$ up to 40, where the laser intensities and the frequencies are scaled from those for $n=1$ in order to maintain a fixed Keldysh parameter $\gamma$$< 1$ for all $n$. We find that as we increase $n$ while keeping $\gamma$ fixed, the position of the cut-off scales in well defined manner. Moreover, a secondary plateau forms with a new cut-off, splitting the HHG plateau into two regions. First of these sub-plateaus is composed of lower harmonics, and has a higher yield than the second one. The latter extends up to the semiclassical $I_p+3.17U_p$ cut-off. We find that this structure is universal, and the HHG spectra look the same for all $n\gtrsim 10$ when plotted as a function of the scaled harmonic order. We investigate the $n$-, $l$- and momentum distributions to elucidate the physical mechanism leading to this universal structure

Phase-dependent interference fringes in the wavelength scaling of harmonic efficiency

We describe phase-dependent wavelength scaling of high-order harmonic generation efficiency driven by ultra-short laser fields in the mid-infrared. We employ both numerical solution of the time-dependent Schr\"{o}dinger equation and the Strong Field Approximation to analyze the fine-scale oscillations in the harmonic yield in the context of channel-closing effects. We show, by varying the carrier-envelope phase, that the amplitude of these oscillations depend strongly on the number of returning electron trajectories. Furthermore, the peak positions of the oscillations vary significantly as a function of the carrier-envelope phase. Owing to its practical applications, we also study the wavelength dependence of harmonic yield in the "single-cycle" limit, and observe a smooth variation in the wavelength scaling originating from the vanishing fine-scale oscillations.Comment: 5 pages, 4 figure

The effect of vascular graft and human umbilical cord blood-derived CD34+ stem cell on peripheral nerve healing

AIM: There are many trials concerning peripheral nerve damage causes and treatment options. Unfortunately, nerve damage is still a major problem regarding health, social and economic issues. On this study, we used vascular graft and human cord blood derived stem cells to find an alternative treatment solution to this problem. MATERIAL AND METHODS: We used 21 female Wistar rats on our study. They were anesthetized with ketamine and we studied right hind limbs. On Group 1, we did a full layer cut on the right sciatic nerve. On Group 2, we did a full layer cut on the right sciatic nerve, and we covered synthetic vascular graft on cut area. On Group 3, we did a full layer cut on right sciatic nerve, and we covered the area with stem cell applied vascular graft. RESULTS: At the end of postoperative 8. weeks, we performed EMG on the rats. When we compared healthy and degenerated areas as a result of EMG, we found significant amplitude differences between the groups on healthy areas whereas there was no significant difference on degenerated areas between the groups. Then we re-opened the operated area again to reveal the sciatic nerve cut area, and we performed electron microscope evaluation. On the stem cell group, we observed that both the axon and the myelin sheet prevented degeneration. CONCLUSION: This study is a first on using synthetic vascular graft and cord blood derived CD34+ cells in peripheral nerve degeneration. On the tissues that were examined with electron microscope, we observed that CD34+ cells prevented both axonal and myelin sheath degeneration. Nerve tissue showed similar results to the control group, and the damage was minimal. © 2018 Ali Yilmaz, Abdullah Topcu, Cagdas Erdogan, Levent Sinan Bir, Barbaros Sahin, Gulcin Abban, Erdal Coskun, Ayca Ozkul

Application of asymptotic waveform evaluation for time domain analysis of nonlinear circuits

Cataloged from PDF version of article.A method is described to exploit asymptotic waveform evaluation (ATNE) in the time-domain analysis of nonlinear circuits by using SPICE models for nonlinear devices such as diodes, transistors, etc. Although AWE has been used for linearized circuits only, the aim is to enhance the accuracy of the simulation while preserving the computational efficiency obtained with AWE and to eliminate the piecewise-linear modelling problem. Practical examples are given to illustrate significant improvements in accuracy. For circuits containing weakly nonlinear devices, it is demonstrated that this method is typically at least one order of magnitude faster than SPICE

Quantum network of neutral atom clocks

We propose a protocol for creating a fully entangled GHZ-type state of neutral atoms in spatially separated optical atomic clocks. In our scheme, local operations make use of the strong dipole-dipole interaction between Rydberg excitations, which give rise to fast and reliable quantum operations involving all atoms in the ensemble. The necessary entanglement between distant ensembles is mediated by single-photon quantum channels and collectively enhanced light-matter couplings. These techniques can be used to create the recently proposed quantum clock network based on neutral atom optical clocks. We specifically analyze a possible realization of this scheme using neutral Yb ensembles.Comment: 13 pages, 11 figure