Showing papers on "Absorption (logic) published in 2010"
TL;DR: Chong et al. as mentioned in this paper showed that a coherent perfect absorber (CPA) can be obtained by reversing the gain with absorption, and thus it generally differs from the lasing medium.
Abstract: In a recent work, Y. D. Chong et al. [Phys. Rev. Lett. 105, 053901 (2010)] proposed the idea of a coherent perfect absorber (CPA) as the time-reversed counterpart of a laser, in which a purely incoming radiation pattern is completely absorbed by a lossy medium. The optical medium that realizes CPA is obtained by reversing the gain with absorption, and thus it generally differs from the lasing medium. Here it is shown that a laser with an optical medium that satisfies the parity-time $(\mathcal{PT})$ symmetry condition $\ensuremath{\epsilon}(\ensuremath{-}\mathbf{r})={\ensuremath{\epsilon}}^{*}(\mathbf{r})$ for the dielectric constant behaves simultaneously as a laser oscillator (i.e., it can emit outgoing coherent waves) and as a CPA (i.e., it can fully absorb incoming coherent waves with appropriate amplitudes and phases). Such a device can thus be referred to as a $\mathcal{PT}$-symmetric CPA laser. The general amplification or absorption features of the $\mathcal{PT}$ CPA laser below lasing threshold driven by two fields are determined.
829 citations
TL;DR: In this article, a least squares method was used to fit Ti concentrations in quartz from all experiments to the simple expression for the P-T dependence of Ti-in-quartz solubility, where R is the gas constant 8.3145 J/K, T is temperature in Kelvin, and M is the mole fraction of TiO2 in quartz.
Abstract: Quartz and rutile were synthesized from silica-saturated aqueous fluids between 5 and 20 kbar and from 700 to 940°C in a piston-cylinder apparatus to explore the potential pressure effect on Ti solubility in quartz. A systematic decrease in Ti-in-quartz solubility occurs between 5 and 20 kbar. Titanium K-edge X-ray absorption near-edge structure (XANES) measurements demonstrate that Ti4+ substitutes for Si4+ on fourfold tetrahedral sites in quartz at all conditions studied. Molecular dynamic simulations support XANES measurements and demonstrate that Ti incorporation onto fourfold sites is favored over interstitial solubility mechanisms. To account for the P–T dependence of Ti-in-quartz solubility, a least-squares method was used to fit Ti concentrations in quartz from all experiments to the simple expression $$ RT\ln X_{{{\text{TiO}}_{ 2} }}^{\text{quartz}} = - 60952 + 1.520 \cdot T(K) - 1741 \cdot P(kbar) + RT\ln a_{{{\text{TiO}}_{ 2} }} $$
where R is the gas constant 8.3145 J/K, T is temperature in Kelvin, $$ X_{{{\text{TiO}}_{ 2} }}^{\text{quartz}} $$
is the mole fraction of TiO2 in quartz and $$ a_{{{\text{TiO}}_{ 2} }} $$
is the activity of TiO2 in the system. The P–T dependencies of Ti-in-quartz solubility can be used as a thermobarometer when used in combination with another thermobarometer in a coexisting mineral, an independent P or T estimate of quartz crystallization, or well-constrained phase equilibria. If temperature can be constrained within ±25°C, pressure can be constrained to approximately ±1.2 kbar. Alternatively, if pressure can be constrained to within ±1 kbar, then temperature can be constrained to approximately ±20°C.
395 citations
TL;DR: In this article, the optical properties of the 1042 nm transition of negatively charged nitrogen-vacancy (NV) centers in type-1b diamond have been investigated and the results indicate that the upper level of this transition couples to the ${m}_{s}=\ifmmode\pm\else\textpm\fi{}1$ sublevels of the $^{3}E$ excited state and is short lived with a lifetime of
Abstract: We report measurements of the optical properties of the 1042 nm transition of negatively charged nitrogen-vacancy (NV) centers in type-1b diamond. The results indicate that the upper level of this transition couples to the ${m}_{s}=\ifmmode\pm\else\textpm\fi{}1$ sublevels of the $^{3}E$ excited state and is short lived with a lifetime of $\ensuremath{\lesssim}1\text{ }\text{ns}$. The lower level is shown to have a temperature-dependent lifetime of 462(10) ns at 4.4 K and 219(3) ns at 295 K. The light-polarization dependence of 1042 nm absorption confirms that the transition is between orbitals of ${A}_{1}$ and $E$ character. The results shed light on the NV level structure and optical pumping mechanism.
194 citations
TL;DR: In this paper, the authors presented two different designs of robust, easily manufactured metamaterial-based films of subwavelength thickness capable of full absorption of incident terahertz radiation at certain frequencies.
Abstract: We present two different designs of robust, easily manufactured metamaterial-based films of subwavelength thickness capable of full absorption of incident terahertz radiation at certain frequencies. Both designs allow a choice between the total absorption of all polarizations or only one linear polarization while the other polarization is reflected. Even if the films are optimized for normal incidence, the absorption remains greater than 99% for angles up to $\ensuremath{\sim}35\ifmmode^\circ\else\textdegree\fi{}$ in the TE and up to $\ensuremath{\sim}65\ifmmode^\circ\else\textdegree\fi{}$ in the TM case. In the first design, the maximum absorption frequency shifts considerably with angle, and in the second design it is independent of angle.
187 citations
TL;DR: In this paper, an infrared magneto-optical study of the highly thermoelectric narrow-gap semiconductor was performed in magnetic fields oriented both parallel and perpendicular to the trigonal axis of this layered material and supplemented with UV-visible ellipsometry to obtain the optical conductivity.
Abstract: We present an infrared magneto-optical study of the highly thermoelectric narrow-gap semiconductor ${\text{Bi}}_{2}{\text{Se}}_{3}$. Far-infrared and midinfrared (IR) reflectance and transmission measurements have been performed in magnetic fields oriented both parallel and perpendicular to the trigonal $c$ axis of this layered material and supplemented with UV-visible ellipsometry to obtain the optical conductivity ${\ensuremath{\sigma}}_{1}(\ensuremath{\omega})$. With lowering of temperature we observe narrowing of the Drude conductivity due to reduced quasiparticle scattering, as well as an increase in the absorption edge due to direct electronic transitions. Magnetic fields $H\ensuremath{\parallel}c$ dramatically renormalize and asymmetrically broaden the strongest far-IR optical phonon, indicating interaction of the phonon with the continuum free-carrier spectrum and significant magnetoelectric coupling. For the perpendicular field orientation, electronic absorption is enhanced, and the plasma edge is slightly shifted to higher energies. In both cases the direct transition energy is softened in magnetic field.
167 citations
TL;DR: In this article, ultraviolet spectra of the high-redshift quasar, HE 2347 - 4342, taken by the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope are reported.
Abstract: We report ultraviolet spectra of the high-redshift (z{sub em} {approx} 2.9) quasar, HE 2347 - 4342, taken by the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope. Spectra in the G130M (medium resolution, 1135-1440 A) and G140L (low resolution, 1030-2000 A) gratings exhibit patchy Gunn-Peterson absorption in the 303.78 A Ly{alpha} line of He II between z = 2.39-2.87 (G140L) and z = 2.74-2.90 (G130M). With COS, we obtain better spectral resolution, higher signal-to-noise ratio (S/N), and better determined backgrounds than previous studies, with sensitivity to abundance fractions x{sub He{sub II}} {approx} 0.01 in filaments of the cosmic web. The He II optical depths from COS are higher than those with the Far Ultraviolet Spectroscopic Explorer and range from {tau}{sub He{sub II}} { =} 5, with a slow recovery in mean optical depth to ({tau}{sub He{sub II}}) {<=} 2 at z < 2.7. The He II/H I optical-depth ratio varies ({eta}{approx} 10-100 for 2.4 < z < 2.73 and {eta} = 5-500 for 2.75 < z < 2.89) on scales {Delta}z {approx}< 0.01 (10.8 Mpc in comoving radial distance at z = 2.8), with numerous flux-transmission windows between 1135 and 1186 A. The Hemore » II absorption extends to 1186.26 A (z = 2.905), including associated absorbers with z{sub abs} {approx} z{sub QSO} and minimal 'proximity effect' of flux transmission at the He II edge. We propose a QSO systemic redshift z{sub QSO} = 2.904 {+-} 0.002, some {Delta}z = 0.019 higher than that derived from O I {lambda}1302 emission. Three long troughs (4-10 A or 25-60 Mpc comoving distance) of strong He II absorption between z = 2.75and2.90 are uncharacteristic of the intergalactic medium if He II reionized at z{sub r} {approx} 3. Contrary to recent indirect estimates (z{sub r} = 3.2 {+-} 0.2) from H I optical depths, the epoch of He II reionization may extend to z {approx}< 2.7.« less
131 citations
TL;DR: In this paper, the authors conducted structure measurements of glass under high pressure up to 100 GPa by an energy-dispersive x-ray diffraction method with synchrotron white x rays.
Abstract: We have conducted structure measurements of ${\text{SiO}}_{2}$ glass under high pressure up to 100 GPa by an energy-dispersive x-ray diffraction method with synchrotron white x rays. X-ray diffraction data indicate that ${\text{SiO}}_{2}$ glass transforms from a fourfold- to a sixfold-coordinated structure at pressures between 20 and 35 GPa, and then behaves as an amorphous polymorph having a sixfold-coordinated structure at least up to 100 GPa. These results are consistent with those of density measurements by an x-ray absorption method with monochromatic x rays, except for the slight difference in the pressure range where the transformation from a fourfold- to a sixfold-coordinated structure is completed. They are also mostly consistent with those of structure measurements by an x-ray diffraction method with monochromatic x rays but some aspects are quantitatively different. It is presumed that the irradiation of white x rays may have relaxed the structure and deviatoric stresses of ${\text{SiO}}_{2}$ glass in this study.
120 citations
TL;DR: In this paper, the Mossbauer spectra and magnetization properties of single-crystalline nanostructures are reported, and the latent magnetization locked within the toroidal spin structure of nanocubes has been released.
Abstract: We report on the M\"ossbauer spectra and magnetization properties of single-crystalline ${({\text{BiFeO}}_{3})}_{x}\text{\ensuremath{-}}{({\text{BaTiO}}_{3})}_{1\ensuremath{-}x}$ solid solution nanostructures in the form of nanocubes, measuring approximately 150 to 200 nm on a side, prepared by a molten salt solid-state reaction method in the compositional range wherein $0.5\ensuremath{\le}x\ensuremath{\le}1$. Powder x-ray diffraction (XRD) and monochromatic synchrotron XRD studies indicate products of high purity, which undergo gradual, well-controlled structural transformations from rhombohedral to tetragonal structures with decreasing ``$x$.'' For all solid solution products, room-temperature magnetization studies exhibit hysteretic behavior with remnant magnetization values of ${M}_{\text{r}}\ensuremath{\ge}0.32\text{ }\text{emu}/\text{g}$, indicating that the latent magnetization locked within the toroidal spin structure of ${\text{BiFeO}}_{3}$ has been released. Room-temperature M\"ossbauer spectra show composition-dependent characteristics with decreasing magnetic hyperfine field values and increasing absorption linewidths due to a decrease in the magnetic exchange interaction strength with decreasing $x$. For the lowest $x=0.5$ composition studied, the M\"ossbauer spectra show paramagnetic behavior, indicating a N\'eel temperature for this composition below 300 K. However, room-temperature magnetization studies with applied fields of up to 50 kOe show hysteretic behavior for all compositions, including the $x=0.5$ composition, presumably due to field-induced ordering. Furthermore, hysteresis loops for all compositions exhibit smaller coercivities at 10 K than at 300 K, an observation that may suggest the presence of magnetoelectric coupling in these systems.
116 citations
TL;DR: The electronic structure and magnetism of Ir 5d5 states in nonmetallic, weakly ferromagnetic BaIrO3 are probed with x-ray absorption techniques and the unusual, atomiclike nature of the 5d moment is driven by a strong spin-orbit interaction in heavy Ir ions.
Abstract: The electronic structure and magnetism of Ir $5{d}^{5}$ states in nonmetallic, weakly ferromagnetic ${\mathrm{BaIrO}}_{3}$ are probed with x-ray absorption techniques. Contrary to expectation, the Ir $5d$ orbital moment is found to be $\ensuremath{\sim}1.5$ times larger than the spin moment. This unusual, atomiclike nature of the $5d$ moment is driven by a strong spin-orbit interaction in heavy Ir ions, as confirmed by the nonstatistical large branching ratio at Ir ${L}_{2,3}$ absorption edges. As a consequence, orbital interactions cannot be neglected when addressing the nature of magnetic ordering in ${\mathrm{BaIrO}}_{3}$. The local moment behavior persists even as the metallic-paramagnetic phase boundary is approached with Sr doping or applied pressure.
110 citations
TL;DR: In this paper, the authors investigated the clustering properties of ~1550 broad-line active galactic nuclei (AGNs) at = 0.25 detected in the ROSAT All-Sky Survey (RASS) through their measured cross-correlation function with ~46,000 Luminous Red Galaxies (LRGs) in the Sloan Digital Sky Survey.
Abstract: We investigate the clustering properties of ~1550 broad-line active galactic nuclei (AGNs) at =0.25 detected in the ROSAT All-Sky Survey (RASS) through their measured cross-correlation function with ~46,000 Luminous Red Galaxies (LRGs) in the Sloan Digital Sky Survey. By measuring the cross-correlation of our AGN sample with a larger tracer set of LRGs, we both minimize shot noise errors due to the relatively small AGN sample size and avoid systematic errors due to the spatially varying Galactic absorption that would affect direct measurements of the auto-correlation function (ACF) of the AGN sample.
The measured ACF correlation length for the total RASS-AGN sample ( =1.5 x 10^(44) erg/s) is r_0=4.3^{+0.4}_{-0.5} h^(-1) Mpc and the slope \gamma=1.7^{+0.1}_{-0.1}. Splitting the sample into low and high L_X samples at L_(0.5-10 keV)=10^(44) erg/s, we detect an X-ray luminosity dependence of the clustering amplitude at the ~2.5 \sigma level. The low L_X sample has r_0=3.3^{+0.6}_{-0.8} h^(-1) Mpc (\gamma=1.7^{+0.4}_{-0.3}), which is similar to the correlation length of blue star-forming galaxies at low redshift. The high L_X sample has r_0=5.4^{+0.7}_{-1.0} h^(-1) Mpc (\gamma=1.9^{+0.2}_{-0.2}), which is consistent with the clustering of red galaxies. From the observed clustering amplitude, we infer that the typical dark matter halo (DMH) mass harboring RASS-AGN with broad optical emission lines is log (M_DMH/(h^(-1) M_SUN)) =12.6^{+0.2}_{-0.3}, 11.8^{+0.6}_{-\infty}, 13.1^{+0.2}_{-0.4} for the total, low L_X, and high L_X RASS-AGN samples, respectively.
97 citations
TL;DR: A femtosecond pump-probe experiment was conducted in this article, where the pump pulse injects a modest density of free carriers by multiphoton absorption, and the extent of the probe-pulse absorption provides a model-independent demonstration that avalanche ionization plays a significant role in free-carrier generation by laser pulses as short as 45 fs.
Abstract: In a femtosecond pump-probe experiment the pump pulse injects a modest density of free carriers by multiphoton absorption. Measuring the nonlinear absorption of the probe pulse we observe exciton-seeded multiphoton ionization. The excitons self-trap in ${\text{SiO}}_{2}$ in $l300\text{ }\text{fs}$ following free-carrier injection and decay biexponentially with lifetimes of $34\ifmmode\pm\else\textpm\fi{}8$ and $338\ifmmode\pm\else\textpm\fi{}67\text{ }\text{ps}$ at room temperature. The extent of the probe-pulse absorption provides a model-independent demonstration that avalanche ionization plays a significant role in free-carrier generation by laser pulses as short as 45 fs. Free-carriers injected into a dielectric from extreme-ultraviolet (XUV) sources created by high harmonic or attosecond pulse generation and then avalanched with a perfectly synchronized infrared (fundamental) probe pulse, can provide a route to nanoscale laser machining.
TL;DR: Polycrystalline tetracene films have been explored using weak ∼ 30 fs visible laser pulses that excite the lowest singlet exciton as well as coherent vibrational motion suggesting such modes control the yield of SF photochemistry.
Abstract: Polycrystalline tetracene films have been explored using weak $\ensuremath{\sim}30\text{ }\text{ }\mathrm{fs}$ visible laser pulses that excite the lowest singlet exciton as well as coherent vibrational motion. Transient difference spectra show a triplet absorption which arises following singlet fission (SF) and persists for 1.6 ns without decay. Adaptive pulse shaping identifies multipulse optimal fields which maximize this absorption feature by $\ensuremath{\sim}20%$. These are comprised of subpulses separated by time delays well correlated with the period of lattice vibrations suggesting such modes control the yield of SF photochemistry.
TL;DR: In this paper, an extended x-ray absorption fine-structure (EXAFS) measurements as a function of temperature was used to quantify the local interatomic distances and their mean-square relative displacements.
Abstract: Local structure of ${\text{FeSe}}_{1\ensuremath{-}x}{\text{Te}}_{x}$ has been studied by extended x-ray absorption fine-structure (EXAFS) measurements as a function of temperature. Combination of Se and $\text{Fe}\text{ }K$ edge EXAFS has permitted to quantify the local interatomic distances and their mean-square relative displacements. The Fe-Se and Fe-Te bond lengths in the ternary system are found to be very different from the average crystallographic Fe-Se/Te distance, and almost identical to the Fe-Se and Fe-Te distances for the binary FeSe and FeTe systems, indicating distinct site occupation by the Se and Te atoms. The results provide a clear evidence of local inhomogeneities and coexisting electronic components in the ${\text{FeSe}}_{1\ensuremath{-}x}{\text{Te}}_{x}$, characterized by different local structural configurations, with direct implication on the fundamental electronic structure of these superconductors.
TL;DR: This work coupled for the first time a total absorption spectrometer to a Penning trap in order to obtain sources of very high isobaric purity and solve a significant part of a long-standing discrepancy in the γ component of the decay heat for 239Pu in the 4-3000 s range.
Abstract: The {beta} feeding probability of {sup 102,104,105,106,107}Tc, {sup 105}Mo, and {sup 101}Nb nuclei, which are important contributors to the decay heat in nuclear reactors, has been measured using the total absorption technique. We have coupled for the first time a total absorption spectrometer to a Penning trap in order to obtain sources of very high isobaric purity. Our results solve a significant part of a long-standing discrepancy in the {gamma} component of the decay heat for {sup 239}Pu in the 4-3000 s range.
TL;DR: In this paper, the authors present strong evidence that the broad, diffuse interstellar bands (DIBs) at 4881 and 5450\,\AA are caused by the $B\,^1$B$_1$\,$\leftarrow$,$X\,€1$A$_ 1$ transition of H$_ 2$CCC (l-C$_3$H$_2$).
Abstract: We present strong evidence that the broad, diffuse interstellar bands (DIBs) at 4881 and 5450\,\AA are caused by the $B\,^1$B$_1$\,$\leftarrow$\,$X\,^1$A$_1$ transition of H$_2$CCC (l-C$_3$H$_2$). The large widths of the bands are due to the short lifetime of the $B\,^1$B$_1$ electronic state. The bands are predicted from absorption measurements in a neon matrix and observed by cavity ring-down in the gas phase and show exact matches to the profiles and wavelengths of the two broad DIBs. The strength of the 5450\,\AA DIB leads to a l-C$_3$H$_2$ column density of $\sim5\times10^{14}$ cm$^{-2}$ towards HD\,183143 and $\sim2\times10^{14}$\,cm$^{-2}$ to HD\,206267. Despite similar values of $E$($B-V$), the 4881 and 5450\,\AA DIBs in HD\,204827 are less than one third their strength in HD\,183143, while the column density of interstellar C$_3$ is unusually high for HD\,204827 but undetectable for HD\,183143. This can be understood if C$_3$ has been depleted by hydrogenation to species such as l-C$_3$H$_2$ towards HD\,183143. There are also three rotationally resolved sets of triplets of l-C$_3$H$_2$ in the 6150$-$6330\,\AA region. Simulations, based on the derived spectroscopic constants and convolved with the expected instrumental and interstellar line broadening, show credible coincidences with sharp, weak DIBs for the two observable sets of triplets. The region of the third set is too obscured by the $\alpha$-band of telluric O$_2$.
TL;DR: In this article, the role of apical oxygen atoms in charge-phonon coupling in undoped cuprates was discussed. But the role was not discussed in the case of cuprates with charge spin coupling.
Abstract: Charge and lattice dynamics caused by photocarrier doping of the undoped cuprates ${\text{Nd}}_{2}{\text{CuO}}_{4}$ and ${\text{La}}_{2}{\text{CuO}}_{4}$ were studied by femtosecond absorption spectroscopy. In both compounds, a metallic state is formed just after photoexcitation and decays within $\ensuremath{\sim}200\text{ }\text{fs}$. Photogenerated electrons and holes are subsequently localized due to charge-spin coupling, producing midgap absorptions at different energies. Charge-phonon coupling also occurs in both compounds. This is more significant for ${\text{La}}_{2}{\text{CuO}}_{4}$ than for ${\text{Nd}}_{2}{\text{CuO}}_{4}$, and leads to higher midgap absorption energies, and slower recombination of polaronic carriers. The role of apical oxygen atoms in charge-phonon coupling in ${\text{La}}_{2}{\text{CuO}}_{4}$ is also discussed.
TL;DR: In this paper, it was shown that the transition from the metastable crystalline phase to the amorphous phase is caused by photoassisted destabilization of the resonant bonding present in the crystaline phase.
Abstract: Subnanosecond time-resolved x-ray absorption measurements have been used to probe dynamical changes in the local structure about Ge atoms in the phase-change alloy ${\text{Ge}}_{2}{\text{Sb}}_{2}{\text{Te}}_{5}$ during the optical recording (amorphization) process using an optical pump and x-ray probe technique to examine the reversible phase transition from the metastable crystalline phase to the amorphous phase. We provide unambiguous evidence that the amorphization process does not proceed via the molten state but is a photoassisted process. We argue that the transition to the amorphous phase is a consequence of photoassisted destabilization of the resonant bonding present in the crystalline phase. This observation challenges the currently existing paradigm of the phase-change process which implicitly assumes the existence of the molten phase as a prerequisite for the creation of the amorphous phase. Implications from this finding are discussed, including the possibility to use the polarization of light as an extra coordinate for data recording.
TL;DR: In this paper, the effects of lanthanum doping on the variations of the off-centering distortion and the orbital mixing of BFO are experimentally studied, in conjunction with first-principles density functional theory (DFT) calculations.
Abstract: The lanthanum (La) modification is known to improve dielectric and magnetic properties of ${\text{BiFeO}}_{3}$ (BFO), a promising room-temperature multiferroic oxide. The effects of La doping on the variations of the off-centering distortion and the orbital mixing of BFO are experimentally studied, in conjunction with first-principles density-functional theory (DFT) calculations. Both the Fe-O bond anisotropy in the ${\text{FeO}}_{6}$-octahedron cage and the off-centering ferroelectric polarization along the hexagonal ${[001]}_{\text{h}}$ are predicted to be substantially reduced by the La doping. These DFT predictions agree with the structural-refinement results obtained from high-resolution x-ray powder-diffraction data. We have shown that the apparent improvement of the polarization-field response is not intrinsic and can be attributed to the reduced leakage current by the La doping. X-ray absorption near-edge structure (XANES) spectroscopy study further indicates that the degree of $\text{Fe}\text{ }3d\text{\ensuremath{-}}4p$ orbital mixing decreases with the La doping. The conclusion deduced from XANES study correlates well with the orbital-resolved density of states which predicts that the La doping increases the number of unoccupied states in the $p$ orbital but suppresses the number of unoccupied states in the $\text{Fe}\text{ }3d$ orbital.
TL;DR: In this article, the authors surveyed the Hubble Space Telescope UV spectra of 49 low-redshift quasars for z = 3sigma{sub W{sub r}} and conducted Monte Carlo completeness tests to measure the unblocked redshift and co-moving path length (DELTAX) over which they were sensitive to C IV doublets of equivalent widths and column densities.
Abstract: We surveyed the Hubble Space Telescope UV spectra of 49 low-redshift quasars for z =3sigma{sub W{sub r}}. We conducted Monte Carlo completeness tests to measure the unblocked redshift (DELTAz) and co-moving path length (DELTAX) over which we were sensitive to C IV doublets of a range of equivalent widths and column densities. The absorber line density of (G = 1+2) doublets is dN{sub C{sub IV}}/dX= 4.1{sup +0.7}{sub -0.6} for log N(C{sup +3}) >= 13.2, and dN{sub C{sub IV}}/dX has not evolved significantly since z = 5. The best-fit power law to the G = 1 frequency distribution of column densities f(N(C{sup +3}))ident tok(N(C{sup +3})/N{sub 0}){sup {alpha}{sub N}} has coefficient k = 0.67{sup +0.18}{sub -0.16} x 10{sup -14} cm{sup 2} and exponent {alpha}{sub N} = -1.50{sup +0.17}{sub -0.19}, where N{sub 0} = 10{sup 14} cm{sup -2}. Using the power-lawmore » model of f(N(C{sup +3})), we measured the C{sup +3} mass density relative to the critical density: OMEGA{sub C{sup +3}}= (6.20{sup +1.82}{sub -1.52})x10{sup -8} for 13 0, with dOMEGA{sub C{sup +3}}/dt{sub age}= (0.42+-0.2)x10{sup -8} Gyr{sup -1}.« less
TL;DR: In this paper, the authors report on the Fermi-LAT observations of the Geminga pulsar, the second brightest non-variable GeV source in the $\gamma$-ray sky and the first example of a radio-quiet gamma-ray pulsar.
Abstract: We report on the \textit{Fermi}-LAT observations of the Geminga pulsar, the second brightest non-variable GeV source in the $\gamma$-ray sky and the first example of a radio-quiet $\gamma$-ray pulsar. The observations cover one year, from the launch of the $Fermi$ satellite through 2009 June 15. A data sample of over 60,000 photons enabled us to build a timing solution based solely on $\gamma$ rays. Timing analysis shows two prominent peaks, separated by $\Delta \phi$ = 0.497 $\pm$ 0.004 in phase, which narrow with increasing energy. Pulsed $\gamma$ rays are observed beyond 18 GeV, precluding emission below 2.7 stellar radii because of magnetic absorption. The phase-averaged spectrum was fitted with a power law with exponential cut-off of spectral index $\Gamma$ = (1.30 $\pm$ 0.01 $\pm$ 0.04), cut-off energy $E_{0}$ = (2.46 $\pm$ 0.04 $\pm$ 0.17) GeV and an integral photon flux above 0.1 GeV of (4.14 $\pm$ 0.02 $\pm$ 0.32) $\times$ 10$^{-6}$ cm$^{-2}$ s$^{-1}$. The first uncertainties are statistical and the second are systematic. The phase-resolved spectroscopy shows a clear evolution of the spectral parameters, with the spectral index reaching a minimum value just before the leading peak and the cut-off energy having maxima around the peaks. Phase-resolved spectroscopy reveals that pulsar emission is present at all rotational phases. The spectral shape, broad pulse profile, and maximum photon energy favor the outer magnetospheric emission scenarios.
TL;DR: In this article, the experimental spectra of the oxygen $K$ edge were used to estimate the band gaps of these materials and compare their results to the range of values available in the literature.
Abstract: The electronic structure in alkaline-earth $Ae\text{O}$ $(Ae=\text{Be},\text{ }\text{Mg},\text{ }\text{Ca},\text{ }\text{Sr},\text{ }\text{Ba})$ and post-transition-metal oxides $Me\text{O}$ $(Me=\text{Zn},\text{ }\text{Cd},\text{ }\text{Hg})$ is probed with oxygen $K$-edge x-ray absorption and emission spectroscopy. The experimental data are compared with density-functional theory electronic-structure calculations. We use our experimental spectra of the oxygen $K$ edge to estimate the band gaps of these materials and compare our results to the range of values available in the literature. From the calculated partial density of states we conclude that the position of main $\text{O}\text{ }K$-edge x-ray emission feature in BeO, SrO, and BaO is defined by the position of the $np$ states of the cation while in the other oxides studied here the main $\text{O}\text{ }K$-edge x-ray emission feature is defined by the position of the $(n\ensuremath{-}1)d$ (for CaO) or $nd$ states of the cation.
TL;DR: In this article, the formation and propagation of three-wave coupled vector optical solitons with ultraslow group velocities in a lifetime-broadened seven-state triple-$\ensuremath{\Lambda}$ atomic system under Raman excitation was investigated.
Abstract: In this article, a theoretical scheme is proposed to investigate the formation and propagation of three-wave coupled vector optical solitons with ultraslow group velocities in a lifetime-broadened seven-state triple-$\ensuremath{\Lambda}$ atomic system under Raman excitation. We show that in the presence of a weak applied magnetic field that removes the degeneracy of the corresponding sublevels of the atomic medium, three continuous-wave control fields with circularly left or right polarized fields induce a quantum interference effect which can largely suppress the absorption of the three low-intensity pulsed fields, that is, the circularly ${\ensuremath{\sigma}}^{\ensuremath{-}}$ (right), the linearly $\ensuremath{\pi}$, and the circularly ${\ensuremath{\sigma}}^{+}$ (left) polarized fields converted from one weak linear-polarized probe field. By means of the standard method of multiple scales, we solve the equations of motion of atomic response and probe-control electromagnetic fields and derive three-coupled nonlinear Schr\"odinger equations that govern the nonlinear evolution of the envelopes of the probe fields in this scheme. We then demonstrate that because of the nonlinear coupling to one another, the three probe fields can evolve into three-wave temporal, group velocity, and amplitude-matched optical solitons under appropriate conditions, which are produced from the delicate balance of the dispersion effects and the self- and cross-phase modulation effects. This scheme may thus pave the way to generate ultraslow vector optical solitons composed of three field components in a highly resonant atomic medium and result in a substantial impact on this field of nonlinear optics.
TL;DR: In this article, the authors measured possible miscalibration of the wavelength scale of the VLT-UVES spectrograph and found two distinct types of calibration shifts needed to correct the Th/Ar wavelength scale.
Abstract: We attempt to measure possible miscalibration of the wavelength scale of the VLT-UVES spectrograph. We take spectra of QSO HE0515-4414 through the UVES iodine cell which contains thousands of well-calibrated iodine lines and compare these lines to the wavelength scale from the standard thorium-argon pipeline calibration. Analyzing three exposures of this z = 1.71 QSO, we find two distinct types of calibration shifts needed to correct the Th/Ar wavelength scale. First, there is an overall average velocity shift of between 100 m s{sup -1} and 500 m s{sup -1} depending upon the exposure. Second, within a given exposure, we find intra-order velocity distortions of 100 m s{sup -1} up to more than 200 m s{sup -1}. These calibration errors are similar to, but smaller than, those found earlier in the Keck HIRES spectrometer. We discuss the possible origins of these two types of miscalibration. We also explore the implications of these calibration errors on the systematic error in measurements of {Delta}{alpha}/{alpha}, the change in the fine-structure constant derived from measurement of the relative redshifts of absorption lines in QSO absorption systems. The overall average, exposure-dependent shifts should be less relevant for fine-structure work, but the intra-order shifts have the potentialmore » to affect these results. Using either our measured calibration offsets or a Gaussian model with sigma of around 90 m s{sup -1}, Monte Carlo mock experiments find errors in {Delta}{alpha}/{alpha} of between 1 x 10{sup -6} N {sup -1/2}{sub sys} and 3 x 10{sup -6} N {sup -1/2}{sub sys}, where N{sub sys} is the number of systems used and the range is due to dependence on how many metallic absorption lines in each system are compared.« less
TL;DR: A new environmental measurement, the effective radiant heat load (ERHL) could be used to assess the effective mean radiant temperature of dairy cows, considered as more reliable than those of Tmr in evaluating the thermal environment in the open field.
Abstract: The goal of the present paper was to assess a method for estimating the thermal radiation absorbed by dairy cows (0.875 Holstein–0.125 Guzerath) on pasture. A field test was conducted with 472 crossbred dairy cows in three locations of a tropical region. The following environmental data were collected: air temperature, partial vapour pressure, wind speed, black globe temperature, ground surface temperature and solar radiation. Average total radiation absorbed by animals was calculated as \( {R_{abs}} = 640.0 \pm 3.1\, W.{m^{ - 2}} \). Absorbed short-wave radiation (solar direct, diffuse and reflected) averaged 297.9 ± 2.7 W m−2; long wave (from the sky and from terrestrial surfaces) averaged 342.1 ± 1.5 W m−2. It was suggested that a new environmental measurement, the effective radiant heat load (ERHL), could be used to assess the effective mean radiant temperature \( \left( {T_{\text{mr}}^* } \right) \). Average \( T_{\text{mr}}^* \) was 101.4 ± 1.2°C, in contrast to the usual mean radiant temperature, \( {T_{mr}} = 65.1 \pm 0.5^\circ C \). Estimates of \( T_{\text{mr}}^* \) were considered as more reliable than those of T mr in evaluating the thermal environment in the open field, because T mr is almost totally associated only with long wave radiation.
TL;DR: In this article, it was shown that the hidden conformal symmetry of the nonextremal dyonic Reissner-Nordstrabaom black hole can be probed by a charged massless scalar field at low frequencies.
Abstract: It is shown that the hidden conformal symmetry, namely $SO(2,2)\ensuremath{\sim}SL(2,R{)}_{L}\ifmmode\times\else\texttimes\fi{}SL(2,R{)}_{R}$ symmetry, of the nonextremal dyonic Reissner-Nordstr\"om black hole can be probed by a charged massless scalar field at low frequencies. The existence of such hidden conformal symmetry suggests that the field theory holographically dual to the four-dimensional Reissner-Nordstr\"om black hole indeed should be a two-dimensional conformal field theory (CFT). Although the associated ${\mathrm{AdS}}_{3}$ structure does not explicitly appear in the near horizon geometry, the primary parameters of the dual ${\mathrm{CFT}}_{2}$ can be exactly obtained without the necessity of embedding the four-dimensional Reissner-Nordstr\"om black hole into five-dimensional spacetime. The duality is further supported by comparing the absorption cross sections and real-time correlators obtained from both the CFT and the gravity sides.
TL;DR: In this article, the effects of Ga on the energy centroids of the $4{f}^{1} and $5{d}^{ 1} configurations are negligible and all effects of the Ga codoping are a consequence of the geometrical distortions it causes.
Abstract: Periodic-boundary-conditions density-functional theory and embedded cluster wave-function theory calculations performed on Ga-doped and Ce,Ga-codoped yttrium aluminum garnet (YAG) ${\text{Y}}_{3}{\text{Al}}_{5}{\text{O}}_{12}$, allowed for the determination of the atomistic structures of these materials when Ga substitutes for Al in octahedral and tetrahedral sites and Ce substitutes for Y, as well as for the shifts of the local excited states of main character $\text{Ce}\text{ }4{f}^{1}$, $\text{Ce}\text{ }5{d}^{1}$, and $\text{Ce}\text{ }6{s}^{1}$ induced by Ga codoping. The experimental blueshift experienced by the lowest $\text{Ce}\text{ }4f\ensuremath{\rightarrow}5d$ absorption upon Ga codoping has been reproduced and it has been found to be caused by the reduction in the effective ligand splitting of the $5{d}^{1}$ manifold, which is due to Ga forcing an anisotropic expansion of the surroundings of Ce. The effects of Ga on the energy centroids of the $4{f}^{1}$ and $5{d}^{1}$ configurations are negligible. The direct electronic effects of Ga are insignificant and all effects of Ga codoping are a consequence of the geometrical distortions it causes. This picture corresponds to a simple model under use and it contrasts with the case of La codoping, where the direct electronic effects of La and the centroid energy shift are responsible for the redshift. The reason for such a different behavior could lie in the distance between the dopant and the Ce impurity, which is shorter for Ce,La:YAG than for Ce,Ga:YAG.
TL;DR: In this article, the Bethe-Salpeter equation was solved on top of a quasiparticle electronic structure for optical absorption in graphite, graphene and bilayer of graphene.
Abstract: We present ab initio many-body calculations of the optical absorption in bulk graphite, graphene and bilayer of graphene Electron-hole interaction is included solving the Bethe-Salpeter equation on top of a $GW$ quasiparticle electronic structure For all three systems, we observe strong excitonic effects at high energy, well beyond the continuum of $\ensuremath{\pi}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{\ast}}$ transitions In graphite, these affect the onset of $\ensuremath{\sigma}\ensuremath{\rightarrow}{\ensuremath{\sigma}}^{\ensuremath{\ast}}$ transitions In graphene, we predict an excitonic resonance at 83 eV arising from a background continuum of dipole forbidden transitions In the graphene bilayer, the resonance is shifted to 96 eV Our results for graphite are in good agreement with experiments
TL;DR: In this article, the spin and orbital angular momentum of a thin Ni film during ultrafast demagnetization was studied by means of x-ray magnetic circular dichroism.
Abstract: We follow the evolution of the spin and orbital angular momentum of a thin Ni film during ultrafast demagnetization, by means of x-ray magnetic circular dichroism. Both components decrease with a $130\ifmmode\pm\else\textpm\fi{}40\text{ }\text{fs}$ time constant upon excitation with a femtosecond laser pulse. Additional x-ray absorption measurements reveal an increase in the spin-orbit interaction by $6\ifmmode\pm\else\textpm\fi{}2\mathrm{%}$ during this process. This experimental observation of a transient change in spin-orbit interaction provides input for the theoretical modeling of the ultrafast demagnetization mechanism.
TL;DR: It is shown that the experimental results obtained for networks with moderate and strong absorption are in good agreement with the ones obtained within the framework of random matrix theory.
Abstract: We present the results of the experimental study of the two-port scattering matrix $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{S}$ elastic enhancement factor ${W}_{S,\ensuremath{\beta}}$ for microwave irregular networks simulating quantum graphs with preserved and broken time reversal symmetry in the presence of moderate and strong absorption. In the experiment, quantum graphs with preserved time reversal symmetry were simulated by microwave networks which were built of coaxial cables and attenuators connected by joints. Absorption in the networks was controlled by the length of microwave cables and the use of microwave attenuators. In order to simulate quantum graphs with broken time reversal symmetry we used the microwave networks with microwave circulators. We show that the experimental results obtained for networks with moderate and strong absorption are in good agreement with the ones obtained within the framework of random matrix theory.
TL;DR: In this paper, the Davydov ansatz with two sets of variational parameters, one for each constituting particle in the exciton-phonon system, and a simplified variant of the DAVydov ${\text{D}}_{1}$ ansatz, also known as the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\text{ D}}$ ansantz, with an additional set of phonon displacement parameters, with a close examination of the variational outputs from the two trial states reveals fine details
Abstract: Following the Dirac-Frenkel time-dependent variational principle, dynamics of a one-dimensional Holstein polaron is probed by employing the Davydov ${\text{D}}_{2}$ ansatz with two sets of variational parameters, one for each constituting particle in the exciton-phonon system, and a simplified variant of the Davydov ${\text{D}}_{1}$ ansatz, also known as the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\text{D}}$ ansatz, with an additional set of phonon displacement parameters. A close examination of variational outputs from the two trial states reveals fine details of the polaron structure and intricacies of dynamic exciton-phonon interactions. Superradiance coherence sizes, speeds of exciton-induced phonon wave packets, linear optical absorption, and polaron energy compositions are also included in the study.