Observation of new Rydberg series in the many-electron transition region of N(2)

Fluorescence excitation spectra produced through photoexcitation of N(2) using synchrotron radiation in the spectral region between 50 and 62.5 nm have been obtained with a resolution of 0.004?nm. A broadband detector (in the 115-180 nm region) was employed to monitor fluorescence originated from neutral excited atomic nitrogen fragments which are produced through direct dissociation processes and predissociation from the well-known many-electron excited Rydberg states. We have identified a new Rydberg series (2 (2)Π(g)) 4sσ, a better resolved Rydberg (D (2)Π(g)) npσ series, and also the prominent Codling series converging to the D (2)Π(g), and C (2)Σ(u) (+) states of N(2) (+), respectively. By normalizing our relative fluorescence intensities to previously measured absolute fluorescence cross-section data we obtain the cross-section data of undispersed fluorescence in the 115-180?nm region. The fluorescence quantum yields for the present photodissociative excitation processes are found to be less than 0.05. The present results may provide important data for our understanding of competitions among the various decay channels of the many-electron transition states of N(2).     

Giant ferroelectric polarization of CaMn7O12 induced by a combined effect of Dzyaloshinskii-Moriya interaction and exchange striction

By extending our general spin-current model to noncentrosymmetric spin dimers and performing density functional calculations, we investigate the causes for the helical magnetic order and the origin of the giant ferroelectric polarization of CaMn7O12. The giant ferroelectric polarization is proposed to be caused by the symmetric exchange striction due to the canting of the Mn4+ spin arising from its strong Dzyaloshinskii-Moriya interaction. Our study suggests that CaMn7O12 may exhibit a novel magnetoelectric coupling mechanism in which the magnitude of the polarization is governed by the exchange striction, but the direction of the polarization by the chirality of the helical magnetic order.     

Finite-State Markov Chain Models for the Intensity of Nakagami Fading

For the design, analysis, and simulation of communication systems with Nakagami-m fading channels, it is very convenient to model the fading by finite-state Markov chains in which the states represent fade levels or signal-to-noise ratios in decibels. Our approach to the development of such Markov chain models is to work with the intensity of the fading process, which is proportional to the logarithm of squared envelope of the faded signal. We demonstrate that all the parameters of the Markov chains can be determined from the bivariate distribution of the intensity of the Nakagami-m fading process. Several analytical results are derived from the bivariate distribution of the intensity, including expressions for the chain’s transition probabilities for both adjacent and nonadjacent states and the asymptotic distribution of the intensity for deep fades. For several values of m, we verify the accuracy of our Markov chain models as simulation tools by comparisons of the state probabilities and level-crossing rates obtained from simulations of the Markov chain with those obtained from our analytical expressions.     

A 0.6 V, 4.32 mW, 68 GHz Low Phase-Noise VCO With Intrinsic-Tuned Technique in 0.13 $mu$m CMOS

An intrinsic-tuned, 68 GHz voltage controlled oscillator (VCO) without an extra on-chip accumulation-mode metal oxide semiconductor (MOS)-varactor is demonstrated in a standard, 0.13 mum CMOS technology. This VCO exhibits phase noises of -98.4 dBc/Hz and -115.2 dBc/Hz at 1 and 10 MHz offset, respectively, along with a tuning range of 4.5 % even under a small power consumption of 4.32 mW. Besides, the highest figure-of-merit (taking frequency tuning range into account) of -182 dBc/Hz under the 1 MHz offset condition is achieved among all previously reported >60 GHz CMOS-based VCOs, which is attributed to the proposed intrinsic tuning mechanism.     

Electronic texture of the thermoelectric oxide Na0.75CoO2

From 59Co and 23Na NMR, we demonstrate the impact of the Na+ vacancy ordering on the cobalt electronic states in Na0.75CoO2: at long time scales, there is neither a disproportionation into 75% Co3+ and 25% Co4+ states, nor a mixed-valence metal with a uniform Co3.25+ state. Instead, the system adopts an intermediate configuration in which 30% of the lattice sites form an ordered pattern of localized Co3+ states. Above 180 K, an anomalous mobility of specific Na+ sites is found to coexist with this electronic texture, suggesting that the formation of the latter may contribute to stabilizing the Na+ ordering. Control of the ion doping in these materials thus appears to be crucial for fine-tuning of their thermoelectric properties.     

Room-temperature ferromagnetism in amorphous In–Ga–Zn–O films fabricated by using pulsed-laser deposition

Room-temperature ferromagnetism (RTFM) was observed in pulsed-laser deposited amorphous In–Ga–Zn–O (a-IGZO) films undoped with impurities containing unpaired d or f electrons. The presence of oxygen vacancies in the prepared a-IGZO films was verified by X-ray photoelectron spectroscopy and suggested to be responsible for the observed RTFM. The electrical and optical properties of the a-IGZO films were also investigated.     

Synthesis of a phosphinated acetoxybenzoic acid and its application in enhancing Tg and flame retardancy of poly(ethylene terephthalate)

A new phosphinated acetoxybenzoic acid, 1‐(4‐acetoxyphenyl)‐1‐(4‐carboxylphenyl)‐1‐(6‐oxido‐6H‐dibenz<c,e><1,2> oxaphosphorin‐6‐yl)ethane (3), was prepared by a three‐step procedure. Phosphinated copolyesters based on the acidolysis and polycondensation of (3) with poly(ethylene terephthalate) (PET) were prepared. The crystallinity of copolyesters decreased gradually with the content of (3), as shown in wide‐angle X‐ray diffractograms and differential scanning calorimetry thermograms. Dynamic mechanical analysis and thermal mechanical analysis show T_g increased with the content of (3). UL‐94 flame retardant test shows that the flame resistance of PET was enhanced with the content of (3), and a copolyester with UL‐94 V‐0 grade can be achieved with a phosphorus content as low as 1.43 wt %. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 424–434     

Free-space electrooptic sampling of terahertz radiation from optically excited superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films

The characteristics of photogenerated terahertz radiation from a current-biased superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) bow-tie antenna were investigated using a free-space electrooptic sampling technique. Picosecond electromagnetic pulses about 450 fs wide were obtained. The frequency spectrum derived by Fourier transforming the picosecond pulses spans over 0.1-4 THz. The dynamics of the quasi-particles optically induced by the ultrafast laser pulse primarily determines the performances of the transient terahertz radiation generated under different operating parameters. The results indicate a characteristic quasi-particle relaxation time of about 2.5 ps close to the critical temperature T/sub c/, and a faster time at lower temperatures.     

Carrier-induced energy shift in GaAs/AlGaAs multiple quantum welllaser diodes

Emission energy shift due to high carrier density at threshold in multiple quantum well (MQW) laser diodes is investigated theoretically. This energy shift is evaluated through the Schrodinger and the Poisson equations self-consistently as well as the calculation of the gain spectra with carrier-dependent lifetime broadening. The band filling and the gain broadening effects show a blue shift on the emission energy. Larger number of wells, lower barrier height, or wider well thickness, reduces the blue shift dependence on the carrier density. At high injections, this blue shift is offset by the bandgap shrinkage effect, which displays smaller influence on MQW's. While the carrier density is further increased, the transition due to the second quantized state is found in single quantum wells, however it is difficult to be observed in MQW's