The First Occurrence in the Fossil Record of an Aquatic Avian Twig-Nest with Phoenicopteriformes Eggs: Evolutionary Implication

14 p.

Optimization of multi-cycle two-color laser fields for the generation of an isolated attosecond pulse

The effect of the mixing of pulsed two color fields on the generation of an isolated attosecond pulse has been systematically investigated. One main color is 800 nm and the other color (or secondary color) is varied from 1.2 to 2.4 mu m. This work shows that the continuum length behaves in a similar way to the behavior of the difference in the square of the amplitude of the strongest and next strongest cycle. As the mixing ratio is increased, the optimal wavelength for the extended continuum shifts toward shorter wavelength side. There is a certain mixing ratio of intensities at which the continuum length bifurcates, i.e., the existence of two optimal wavelengths. As the mixing ratio is further increased, each branch bifurcates again into two sub-branches. This 2D map analysis of the mixing ratio and the wavelength of the secondary field easily allows one to select a proper wavelength and the mixing ratio for a given pulse duration of the primary field. The study shows that an isolated sub-100 attosecond pulse can be generated mixing an 11 fs full-width-half-maximum (FWHM), 800 laser pulse with an 1840 nm FWHM pulse. Furthermore the result reveals that a 33 fs FWHM, 800 nm pulse can produce an isolated pulse below 200 as, when properly mixed. (c) 2008 Optical Society of America.

A plasma channel scheme for the interaction of an intense femtosecond laser pulse with a deuterium cluster jet

We propose a plasma channel scheme to obtain an improved table-top laser driven fusion neutron yield as a result of explosions of large deuterium clusters irradiated by an intense laser pulse. A cylindrical plasma channel is created by two moderate intensity laser prepulses at the edge of a deuterium cluster jet along which an intense main laser pulse propagates several nanoseconds later. With the aid of this plasma channel, the main laser pulse will be allowed to deposit its energy into the central region of the deuterium gas jet where the cluster sizes are larger and the atomic density is higher. The plasma channel formation and its impact on the deuterium ion energy spectrum and the consequent fusion neutron yield have been investigated. The calculated results show that a remarkable increase of the table-top laser driven fusion neutron yield would be expected.

Origin of the double-peak structure in longitudinal momentum distributions for single ionization of an He atom in strong laser field

The single ionization of an He atom by intense linearly polarized laser field in the tunneling regime is studied by S- matrix theory. When only the first term of the expansion of the S matrix is considered and time, spatial distribution, and fluctuation of the laser pulse are taken into account, the obtained momentum distribution in the polarization direction of laser field is consistent with the semiclassical calculation, which only considers tunneling and the interaction between the free electron and external field. When the second term, which includes the interaction between the core and the free electron, is considered, the momentum distribution shows a complex multipeak structure with the central minimum and the positions of some peaks are independent of the intensity in some intensity regime, which is consistent with the recent experimental result. Based on our analysis, we found that the structures observed in the momentum distribution of an He atom are attributed to the " soft" collision of the tunneled electron with the core.

The Riesz space structure of an Abelian W*-algebra

Let M be an Abelian W*-algebra of operators on a Hilbert space H. Let M₀ be the set of all linear, closed, densely defined transformations in H which commute with every unitary operator in the commutant M’ of M. A well known result of R. Pallu de Barriere states that if ɸ is a normal positive linear functional on M, then ɸ is of the form T → (Tx, x) for some x in H, where T is in M. An elementary proof of this result is given, using only those properties which are consequences of the fact that ReM is a Dedekind complete Riesz space with plenty of normal integrals. The techniques used lead to a natural construction of the class M₀, and an elementary proof is given of the fact that a positive self-adjoint transformation in M₀ has a unique positive square root in M₀. It is then shown that when the algebraic operations are suitably defined, then M₀ becomes a commutative algebra. If ReM₀ denotes the set of all self-adjoint elements of M₀, then it is proved that ReM₀ is Dedekind complete, universally complete Riesz spaces which contains ReM as an order dense ideal. A generalization of the result of R. Pallu de la Barriere is obtained for the Riesz space ReM₀ which characterizes the normal integrals on the order dense ideals of ReM₀. It is then shown that ReM₀ may be identified with the extended order dual of ReM, and that ReM₀ is perfect in the extended sense.

Some secondary questions related to the Riesz space ReM are also studied. In particular it is shown that ReM is a perfect Riesz space, and that every integral is normal under the assumption that every decomposition of the identity operator has non-measurable cardinal. The presence of atoms in ReM is examined briefly, and it is shown that ReM is finite dimensional if and only if every order bounded linear functional on ReM is a normal integral.

Thermodynamic and kinetic behavior of an argon plasma jet. Decomposition of nitric oxide between 1300 - 1750 degrees K in an argon plasma

In the first part of the study, an RF coupled, atmospheric pressure, laminar plasma jet of argon was investigated for thermodynamic equilibrium and some rate processes.

Improved values of transition probabilities for 17 lines of argon I were developed from known values for 7 lines. The effect of inhomogeneity of the source was pointed out.

The temperatures, T, and the electron densities, n_e , were determined spectroscopically from the population densities of the higher excited states assuming the Saha-Boltzmann relationship to be valid for these states. The axial velocities, v_z, were measured by tracing the paths of particles of boron nitride using a three-dimentional mapping technique. The above quantities varied in the following ranges: 10¹² ˂ n_e ˂ 10¹⁵ particles/cm³, 3500 ˂ T ˂ 11000 °K, and 200 ˂ v_z ˂ 1200 cm/sec.

The absence of excitation equilibrium for the lower excitation population including the ground state under certain conditions of T and n_e was established and the departure from equilibrium was examined quantitatively. The ground state was shown to be highly underpopulated for the decaying plasma.

Rates of recombination between electrons and ions were obtained by solving the steady-state equation of continuity for electrons. The observed rates were consistent with a dissociative-molecular ion mechanism with a steady-state assumption for the molecular ions.

In the second part of the study, decomposition of NO was studied in the plasma at lower temperatures. The mole fractions of NO denoted by x_NO were determined gas-chromatographically and varied between 0.0012 ˂ x_NO ˂ 0.0055. The temperatures were measured pyrometrically and varied between 1300 ˂ T ˂ 1750°K. The observed rates of decomposition were orders of magnitude greater than those obtained by the previous workers under purely thermal reaction conditions. The overall activation energy was about 9 kcal/g mol which was considerably lower than the value under thermal conditions. The effect of excess nitrogen was to reduce the rate of decomposition of NO and to increase the order of the reaction with respect to NO from 1.33 to 1.85. The observed rates were consistent with a chain mechanism in which atomic nitrogen and oxygen act as chain carriers. The increased rates of decomposition and the reduced activation energy in the presence of the plasma could be explained on the basis of the observed large amount of atomic nitrogen which was probably formed as the result of reactions between excited atoms and ions of argon and the molecular nitrogen.

Efficient minimum manoeuvre time optimisation of an oversteering vehicle at constant forward speed

A receding horizon steering controller is presented, capable of pushing an oversteering nonlinear vehicle model to its handling limit while travelling at constant forward speed. The controller is able to optimise the vehicle path, using a computationally efficient and robust technique, so that the vehicle progression along a track is maximised as a function of time. The resultant method forms part of the solution to the motor racing objective of minimising lap time. © 2011 AACC American Automatic Control Council.

Modification of the trapped field in bulk high-temperature superconductors as a result of the drilling of a pattern of artificial columnar holes

The trapped magnetic field is examined in bulk high-temperature superconductors that are artificially drilled along their c-axis. The influence of the hole pattern on the magnetization is studied and compared by means of numerical models and Hall probe mapping techniques. To this aim, we consider two bulk YBCO samples with a rectangular cross-section that are drilled each by six holes arranged either on a rectangular lattice (sample I) or on a centered rectangular lattice (sample II). For the numerical analysis, three different models are considered for calculating the trapped flux: (i), a two-dimensional (2D) Bean model neglecting demagnetizing effects and flux creep, (ii), a 2D finite-element model neglecting demagnetizing effects but incorporating magnetic relaxation in the form of an E-J power law, and, (iii), a 3D finite element analysis that takes into account both the finite height of the sample and flux creep effects. For the experimental analysis, the trapped magnetic flux density is measured above the sample surface by Hall probe mapping performed before and after the drilling process. The maximum trapped flux density in the drilled samples is found to be smaller than that in the plain samples. The smallest magnetization drop is found for sample II, with the centered rectangular lattice. This result is confirmed by the numerical models. In each sample, the relative drops that are calculated independently with the three different models are in good agreement. As observed experimentally, the magnetization drop calculated in the sample II is the smallest one and its relative value is comparable to the measured one. By contrast, the measured magnetization drop in sample (1) is much larger than that predicted by the simulations, most likely because of a change of the microstructure during the drilling process.

Carbon and nitrogen metabolism of an eutrophication tolerative macrophyte, Potamogeton crispus, under NH4+ stress and low light availability

Submersed macrophytes in eutrophic lakes often experience high NH4+ concentration and low light availability in the water column. This study found that an NH4+-N concentration of 1 mgL(-1) in the water column apparently caused physiological stress on the macrophyte Potamogeton crispus; L The plants accumulated free amino acids (FAA) and lost soluble carbohydrates (SC) under NH4+ stress. These stressful effects of NH4+ were exacerbated under low light availability. Shading significantly increased NH4+ and FAA contents and dramatically decreased SC and starch contents in the plant shoots. At an NH4+-N concentration of 1 mg L-1 in the water column, neither growth inhibition nor NH4+ accumulation was observed in the plant tissues of P. crispus under normal light availability. The results showed that 1 mg L-1 NH4+-N in the water column was not toxic to P. crispus in a short term. To avoid NH4+ toxicity. active NH4+ transportation out of the cell may cost energy and thus result in a decline of carbohydrate. When NH4+ inescapably accumulates in the plant cell, i.e. under NH4+ Stress and shading, NH4+ is scavenged by FAA synthesis. (c) 2009 Published by Elsevier B.V.

Ex situ conservation status of an endangered Yangtze finless porpoise population (Neophocaena phocaenoides asiaeorientalis) as measured from microsatellites and mtDNA diversity

The Yangtze finless porpoise, Neophocaena phocaenoides asiaeorientalis, is all endangered small cetacean that occurs only in the middle and lower reaches of the Yangtze River of China. The establishment of a breeding population of the porpoise in Tian-e-Zhou Baiji National Natural Reserve represents the first attempt at ex situ conservation efforts for a cetacean species. With the goal of effective protection, management, and monitoring of this preserved population, we examined its genetic diversity using 930 bp of mtDNA control region sequences and 13 polymorphic microsatellite loci. A very low level of genetic variation (h = 0.6010 +/- 0.0029 s.d.; pi = 0.0007 +/- 0.0000002 s.d.) in the mtDNA control region sequences and a moderate genetic diversity (Ho = 0.5740 +/- 0.2575 s.d.) in the microsatellites were detected in the population. It is necessary to introduce more individuals with representative genetic variations into the reserve ill order to foml a larger and healthier group structure for long-term survival of the population. Successful establishment of the Yangtze finless porpoise population in the Reserve also provides a useful model for an ex situ conservation programme for other rare and endangered species. (c) 2005 International Council for the Exploration ofthe Sea. Published by Elsevier Ltd. All rights reserved.

The low TN : TP ratio, a cause or a result of Microcystis blooms?

An enclosure experiment in the shallow, subtropical Lake Donghu, China, was performed in the summer of 2001 to examine the effect of TN:TP (total phosphorus) ratios and P-reduction on the occurrence of Microcysitis blooms. The treatments were performed with enough amounts of N but with different amounts of P in the water column and sediment. Microcystis blooms occurred in the enclosures either with an initial TN:TP <29 or TN:TP >29 where the nutrients (N, P) were high enough. Microcysitis blooms never occurred in the treatments with low P concentration in spite of the presence of sufficient N. The P-rich sediments served as an important source for the P supply in the water column, and such a process was activated greatly by the outburst of Microcystis blooms which pumped up selectively P from the sediments and thus decreased the TN:TP ratios. Therefore, the low TN:TP ratio is not a cause but rather a result of Microcystis blooms. (C) 2002 Elsevier Science Ltd. All rights reserved.

Output Characteristics of an InP/InGaAsP Triangle Microcavity Laser

Mode competitions between modes with different output coupling efficiencies can result in optical bistability under certain asymmetric nonlinear gain. For a GaInAsP/InP equilateral triangle microlaser with the side length of 10 mu m, the drop of the output power with the increase of the injection current is observed corresponding to transverse mode transitions. Furthermore, the measured laser spectra up to 270 K show that lasing modes coexist with the wavelength interval of 39 nm at 240 K. The emission at 5.2 THz can be expected by the mode frequency beating with the 39 nm interval.

The design algorithm of an associative memory neural network

A design algorithm of an associative memory neural network is proposed. The benefit of this design algorithm is to make the designed associative memory model can implement the hoped situation. On the one hand, the designed model has realized the nonlinear association of infinite value pattern from n dimension space to m dimension space. The result has improved the ones of some old associative memory neural network. On the other hand, the memory samples are in the centers of the fault-tolerant. In average significance the radius of the memory sample fault-tolerant field is maximum.

A complex Fourier transformation study of the contactless electroreflectance of an undoped-n(+) GaAs structure

Complex Fourier transformation (CFT) has been employed to analyse contactless electroreflectance (CER) spectra from an undoped-n(+) GaAs structure with various ac modulations and dc bias voltages. The CFT spectra of CER have been compared with those of photoreflectance (PR). It has been found that the CER non-flat modulation is between the built-in electric field and a larger electric field which increases with the modulation voltage. The result has been explained by the screening of the applied modulation electric field in one of the two half modulation cycles and the trapping of electrons in surface states in the other half modulation cycle. The dc bias does not change the CER spectra, hence their CFT spectra. This is because of the screening of the applied dc bias electric field.

Isolated sub-30-as pulse generation of an He+ ion by an intense few-cycle chirped laser and its high-order harmonic pulses

We present an efficient method to generate a ultrashort attosecond (as) pulse when a model He+ ion is exposed to the combination of an intense few-cycle chirped laser pulse and its 27th harmonics. By solving the time-dependent Schroumldinger equation, we found that high-order harmonic generation (HHG) from He+ ion is enhanced by seven orders of magnitude due to the presence of the harmonic pulse. After optimizing the chirp of the fundamental pulse, we show that the cut-off energy of the generated harmonics is extended effectively to I-p+25.5U(p). As a result, an isolated 26-as pulse with a bandwidth of 170.5 eV can be obtained directly from the supercontinuum around the cut-off of HHG. To better understand the physical origin of HHG enhancement and attosecond pulse emission, we perform semiclassical simulations and analyze the time-frequency characteristics of attosecond pulse.