Absorption (logic)

About: Absorption (logic) is a research topic. Over the lifetime, 5733 publications have been published within this topic receiving 236302 citations.

Self-Organizing GeV, Nanocoulomb, Collimated Proton Beam from Laser Foil Interaction at 7 X 1021 W/cm2

Abstract: We report on a self-organizing, quasistable regime of laser proton acceleration, producing 1 GeV nanocoulomb proton bunches from laser foil interaction at an intensity of $7\ifmmode\times\else\texttimes\fi{}{10}^{21}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$. The results are obtained from 2D particle-in-cell simulations, using a circular polarized laser pulse with Gaussian transverse profile, normally incident on a planar, 500 nm thick hydrogen foil. While foil plasma driven in the wings of the driving pulse is dispersed, a stable central clump with $1--2\ensuremath{\lambda}$ diameter is forming on the axis. The stabilization is related to laser light having passed the transparent parts of the foil in the wing region and enfolding the central clump that is still opaque. Varying laser parameters, it is shown that the results are stable within certain margins and can be obtained both for protons and heavier ions such as ${\mathrm{He}}^{2+}$.

Terahertz carpet cloak based on a ring resonator metasurface

Abstract: In this work we present the concept and design of an ultrathin (\ensuremath{\lambda}/22) terahertz (THz) unidirectional carpet cloak based on the local phase compensation approach enabled by gradient metasurfaces. A triangular surface bump with center height of 4.1 mm (1.1\ensuremath{\lambda}) and tilt angle of 20\ifmmode^\circ\else\textdegree\fi{} is covered with a metasurface composed of an array of suitably designed closed ring resonators with a transverse gradient of surface impedance. The ring resonators provide a wide range of control for the reflection phase with small absorption losses, enabling efficient phase manipulation along the edge of the bump. Our numerical results demonstrate a good performance of the designed cloak in both near field and far field, and the cloaked object mimics a flat ground plane within a broad range of incidence angles, over 35\ifmmode^\circ\else\textdegree\fi{} angular spectrum centered at 45\ifmmode^\circ\else\textdegree\fi{}. The presented cloak design can be applied in radar and antenna systems as a thin, lightweight, and easy to fabricate solution for radio and THz frequencies.

Cosine and other terms in the Josephson tunneling current

Abstract: To second order in perturbation theory the tunneling current between two superconductors can be expressed as follows: $I(V,T)={I}_{J1}(V,T)sin\ensuremath{\phi}+{I}_{J2}(V,T)cos\ensuremath{\phi}+{I}_{\mathrm{qp}}(V,T),$ where $V$ is a constant voltage across the tunneling barrier, $T$ is the temperature, and $\ensuremath{\phi}=\ensuremath{-}\frac{2eVt}{\ensuremath{\hbar}}+{\ensuremath{\phi}}_{0}$ is the difference in the phases of the wave functions of the superconductors on each side of the barrier. Numerical evaluations of each of the terms are presented as functions of voltage for several temperatures. For the second term we find a different sign from that found in previous numerical work. When the superconductors on each side of the tunneling barrier are different, structure occurs at a voltage corresponding to the difference in the energy gaps. For the first two terms this structure was previously unrecognized. In addition, it is shown that the term in $cos\ensuremath{\phi}$ has no effect upon rf-induced steps in the time-averaged current-voltage curve for a tunneling junction biased by a voltage source. Finally a relation is discussed between tunneling and other experiments such as far-infrared absorption and acoustic attenuation in superconductors. It is shown that tunneling can be thought of in terms of a slight generalization of the coherence effects which dominate the other kinds of experiments.

The First Observations of Low-redshift Damped Lyα Systems with the Cosmic Origins Spectrograph

Abstract: We report on the first Cosmic Origins Spectrograph observations of damped Ly{alpha} systems (DLAs) and sub-damped Ly{alpha} systems (sub-DLAs) discovered in a new survey of the gaseous halos of low-redshift galaxies. From observations of 37 sightlines, we have discovered three DLAs and four sub-DLAs. We measure the neutral gas density {Omega}{sub HI}, and redshift density d N/d z, of DLA and sub-DLA systems at z < 0.35. We find d N/dz = 0.25{sup +0.24}-{sub 0.14} and {Omega}{sub HI} = 1.4{sup +1.3}{sub -0.7} x 10{sup -3} for DLAs, and d N/d z = 0.08{sup +0.19}{sub -0.06} with {Omega}{sub HI} = 4.2{sup +9.6}{sub -3.5} x 10{sup -5} for sub-DLAs over a redshift path {Delta}z = 11.9. To demonstrate the scientific potential of such systems, we present a detailed analysis of the DLA at z{sub abs} = 0.1140 in the spectrum of SDSS J1009+0713. Profile fits to the absorption lines determine log N(H I) = 20.68 {+-} 0.10 with a metallicity determined from the undepleted element sulfur of [S/H] = -0.62 {+-} 0.18. The abundance pattern of this DLA is similar to that of higher z DLAs, showing mild depletion of the refractory elements Fe and Ti with [S/Fe] = +0.24 {+-} 0.22more » and [S/Ti] = +0.28 {+-} 0.15. Nitrogen is underabundant in this system with [N/H] = -1.40 {+-} 0.14, placing this DLA below the plateau of the [N/{alpha}] measurements in the local universe at similar metallicities. This DLA has a simple kinematic structure with only two components required to fit the profiles and a kinematic width of {Delta}v{sub 90} = 52 km s{sup -1}. Imaging of the QSO field with the Hubble Space Telescope/Wide Field Camera 3 reveals a spiral galaxy at very small impact parameter to the QSO and several galaxies within 10'', or 20 comoving kpc at the redshift of the DLA. Follow-up spectra with the Low Resolution Imaging Spectrometer on the Keck telescope reveal that none of the nearby galaxies are at the redshift of the DLA. The spiral galaxy is identified as the host galaxy of the QSO based on the near perfect alignment of the nucleus and disk of the galaxy as well as spectra of an H II region showing emission lines at the QSO redshift. A small feature appears 0.''70 from the nucleus of the QSO after point-spread function subtraction, providing another candidate for the host galaxy of the DLA system. Even with these supporting data, we are unable to unambiguously identify the host galaxy of the DLA, exemplifying some of the difficulties in determining DLA hosts even at low redshift.« less

Optical Studies of Alkali Fluorides and Alkaline Earth Fluorides in VUV Region

Abstract: The results of a series of reflectivity and absorption measurements performed to clarify respectively the excitonic transitions in the intrinsic region to 13.5 eV and the thermal and spectral dependences of absorptions in the tail region of LiF, NaF, KF, CaF 2 SrF 2 and BaF 2 , each being cleaved from Harshaw blocks of single crystal, are presented. The tails of Harshaw LiF, being expressed by exponential functions of energy in the range of 10 0 cm -1 \({\lesssim}A{\lesssim}5{\cdot}10^{2}\) cm -1 and 300°K≤ T ≤573°K, have turned out to be extrinsic to LiF. The present experiments could not provide sufficiently conclusive evidences in clarifying the question whether the tails of Harshaw alkaline earth fluorides, to Urbach rule is applicable for the range of 10 0 cm -1 \({\lesssim}A{\lesssim}10^{2}\) cm -1 and 78°K≤ T ≤573°K, are intrinsic. In the first peak of reflectivity spectra, the fluorine doublet with ∼0.05 eV separation is detected for KF and quintet structure for SrF 2 and BaF 2 . In the latter, th...