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In this paper, which is of programmatic rather than quantitative nature, weaim to further delineate and sharpen the future potential of the LISA missionin the area of fundamental physics. Given the very broad range of topics thatmight be relevant to LISA, we present here a sample of what we view asparticularly promising directions, based in part on the current researchinterests of the LISA scientific community in the area of fundamental physics.We organize these directions through a "science-first" approach that allows usto classify how LISA data can inform theoretical physics in a variety of areas.For each of these theoretical physics classes, we identify the sources that arecurrently expected to provide the principal contribution to our knowledge, andthe areas that need further development. The classification presented hereshould not be thought of as cast in stone, but rather as a fluid framework thatis amenable to change with the flow of new insights in theoretical physics.

A paraxial optical propagation code is developed, which can be combined with various existing models of gain media, to model oscillators with full paraxial wave propagation within the resonator. The diffraction losses are a considerable part of the single-pass cavity loss for free-electron laser for infrared experiments (FELIX ) and it is shown that a resonator with hole coupling might be a viable alterative to a standard resonator with transmissive optics for the high gain vacuum ultraviolet free-electron laser (VUV-FEL) oscillator.

We determine the size of argon clusters generated with a planar nozzle, based on the optical measurements in conjunction with theoretical modelling. Using a quasi-one dimensional model for the moments of the cluster size distribution, we determine the influence of critical physical assumptions. These refer to the surface tension depending on the presence of thermal equilibrium, the mass density of clusters, and different methods to model the growth rate of the cluster radius. We show that, despite strong variation in the predicted cluster size, ⟨N⟩, the liquid mass ratio, g, can be determined with high trustworthiness, because g is predicted as being almost independent of the specific model assumptions. Exploiting this observation, we use the calculated value for g to retrieve the cluster size from optical measurements, i.e., calibrated Rayleigh scattering and interferometry. Based on the measurements of the cluster size vs. the nozzle stagnation pressure, we provide a new power law for the prediction of the cluster size in experiments with higher values of the Hagena parameter (Γ*>104). This range is of relevance for experiments on high-intensity laser matter interactions. [ABSTRACT FROM AUTHOR]

We present detailed measurements on the x-ray preionization electron density in a discharge chamber filled with different gases relevant to discharge pumped high-pressure excimer lasers. By comparing experimental results with the theoretical electron densities, we conclude that the observed preionization is inconsistent with the standard picture of direct ionization through x-ray absorption in the gas. We conclude that depending on the gas pressure, type of gas, and the gap length between the discharge electrodes used, x-ray preionization in excimer gases is, to a significant extent or even dominantly, based on a different mechanism. We identify that this mechanism is based on fast photoelectrons emitted by the cathode into the discharge chamber. [ABSTRACT FROM AUTHOR]

The net gain is measured for various pump power densities in a discharge-pumped long-pulse KrCl laser (222 nm). For this, a three-electrode laser system is employed, which is operated at high gas pressures of around 3.5 bar with pump power densities of 300-650 kW cm-3. The net gain reaches a maximum of 1.6% cm-1. Using the experimental results, values are calculated for the small-signal gain, the losses, and the saturation intensity. The losses and the saturation intensity are found to increase much stronger with the excitation rate than the small-signal gain. Fluorescence measurements at 222 nm show that the upper laser level depopulates faster when the power density increases. The influence of collisional quenching and the halogen consumption on the laser performance are discussed. [ABSTRACT FROM AUTHOR]

The discharge homogeneity in F2-based excimer laser gas mixtures and its dependence on various key parameters, such as the degree of preionization, preionization delay time, F2 concentration and current density, is investigated in a small x-ray preionized discharge chamber. The spatial and temporal evolution of the discharges is monitored by taking photographs of the discharge fluorescence with a fast intensified CCD camera. It is found that a preionization electron density of about 107 cm-3 bar-1 is sufficient to initiate a streamer-free homogeneous discharge in gas mixtures of helium and fluorine with multiatmospheric gas pressure. The accompanying optimum time delay between the application of the x-ray pulse and voltage across the discharge electrodes is determined to be about 20 ns. It is shown that in spite of these optimum initial conditions, a homogeneous glow discharge eventually transforms into an inhomogeneous discharge containing numerous filaments. Our experiments show that the higher the initial F2 concentration, the initial current density or the pump power density, the shorter the time interval over which the discharge stays homogeneous. By a quantitative characterization and defining a detailed measure of the observed discharge inhomogeneity we find that halogen depletion, as suggested from the theory, is responsible for the temporal instability of discharges in such laser gas mixtures, as the experimental results are in good agreement with the theory on the halogen depletion instability mechanism. [ABSTRACT FROM AUTHOR]

In this article we present a theoretical investigation on an experimental design of a laser wakefield accelerator in which electron bunches from a photocathode radio frequency linac are injected into a capillary discharge plasma channel just in front of a few tens of terawatt drive laser pulse. The electron bunch, with a kinetic energy of 2.9 MeV and an energy chirp imposed by the linac, is magnetically compressed by a factor of 8 to a duration of 250 fs, and is magnetically focused into the plasma channel where it matches the spot size of the drive laser (≈30 μm). The dynamics of the bunch, starting from the photocathode, through the linac, along the beam transportation line, through the magnetic compressor, and its focusing into the plasma channel are comprehensively simulated with the general particle tracer code. Further, we use our three-dimensional numerical codes to calculate the laser wakefield and to determine and optimize the trapping and acceleration of the injected bunch in the wakefield. We show that, injecting a 5 pC electron bunch of 250 fs duration, the experiment should deliver an electron bunch of approximately 744 MeV energy, with 1.1% relative energy spread, and with an extremely short duration (6 fs), after acceleration in a 5.4 cm long plasma channel. [ABSTRACT FROM AUTHOR]

We report on the influence that waveguide-induced fluctuations in the phase velocity of the radiation wave have on the gain of Cherenkov-type free-electron lasers. We theoretically analyze low-gain Cherenkov free-electron lasers with a compact design that require resonator feedback for operation. We find that even small spatial variations of the waveguide parameters along the propagation direction can lead to significant degradation of the gain, and we present typical values for the required degree in waveguide precision that would eliminate such effects. [ABSTRACT FROM AUTHOR]

The influence of a plasma density gradient on ions accelerated along the specular (back reflection) direction in the transparent Target Normal Sheath Acceleration regime is investigated. Enhanced acceleration of ions is experimentally observed in this regime using high-intensity and ultra-high contrast laser pulses and extremely thin foils of few nanometer thicknesses. The experimental trend for the maximum proton energy appeared quite different from the already published numerical results in this regime where an infinitely steep plasma gradient was assumed. We showed that for a realistic modelling, a finite density gradient has to be taken into account. By means of particle-incell (PIC) simulations, we studied for the first time the influence of the plasma density scale length on ion acceleration from these nanofoil targets. Through a qualitative agreement between our numerical particle-in-cell simulations and our experiments, the main conclusion with regard to the experimental requirements is that, in the transparent regime evidenced with nanofoils as compared to the opaque regime, the plasma expansion has to be taken into account and both the pulse contrast and the damage threshold of the material are essential parameters. [ABSTRACT FROM AUTHOR]

The article looks at methods used to enhance antibody yield, focusing on the optimal seeding concentrations of hybridomas. It is believed that laboratory techniques used to increase the yield of monoclonal antibodies (MAbs) can be applied to the production of antibodies on a larger scale. Human endogenous retrovirus antibody-producing cell lines used on laboratory mice are discussed.

External injection of an electron bunch in the laser wakefield can result in femtosecond accelerated bunches with relatively low energy spread. In this paper it is shown that the density transition from vacuum to plasma can play an important role in the trapping process. The plasma wavelength in this transition region changes continuously, which means that the injected electrons see an altering wakefield. This can result in strong defocusing of the injected bunch. It is found that the effect becomes stronger for stronger wakefields, longer transition lengths, and lower injection energies. The transition region can be avoided if the bunch is injected into the wakefield at an angle. Injecting the bunch at an angle allows the bunch to be wider and results in more charge being trapped. The dynamics of the bunch in this case are similar to the dynamics of a bunch injected in front of the laser pulse. [ABSTRACT FROM AUTHOR]

A proposal for a self-seeding, tunable free-electron laser amplifier operating in the vacuum ultra-violet (VUV) region of the spectrum is presented. Full three-dimensional (3D) modelling of the free electron laser and the optical feedback system has been carried out. Simulations demonstrate the generation of near transform limited radiation pulses with peak powers in the hundreds of megawatts. Preliminary 1D simulations show that by using a similar system it may be possible to extend such operation beyond the VUV to higher photon energies. [ABSTRACT FROM AUTHOR]

We describe a continuous-wave master-oscillator power-amplifier system based on a distributed Bragg reflection diode laser and an Yb doped fiber amplifier. The observed optical spectrum of the amplified seed source can be tailored to arbitrary shapes and widths between 30 MHz and greater than 1 GHz by controlling the radio frequency modulation wave form of the injection current. [ABSTRACT FROM AUTHOR]

Objective. To gain a better understanding of how low-income fathers of young children think about their role as fathers, we conducted a qualitative inquiry into the beliefs of fathers of 24-month-old children about what 'good fatherhood' means to them. Design. The 575 open-ended interviews, collected in 14 Early Head Start Fathers of Toddlers Qualitative Interview Substudy sites around the United States were analyzed using NUD*IST qualitative software to code and categorize the various roles fathers identified as important to them and their children. Results. Four broad types of roles were identified: (1) providing a stable environment (e.g., providing a living, 'being there' emotionally and physically), (2) teaching (e.g., giving guidance, exposing their child to the world), (3) physical interaction (e.g., play, caregiving), and (4) emotional support (e.g., providing love, building self-esteem). Conclusion. The beliefs of these men are considered in the context of historical perceptions of fatherhood, as well as their implications for generative theories of fatherhood. Overall, fathers articulated a strong sense of commitment and intentionality in their plans for interactions with their children. Our findings provide opportunities for service providers and policymakers to develop positive strategies to ensure fathers' ability to carry out their intentions. [ABSTRACT FROM AUTHOR]

In this introductory article to the Special Issue, we provide an overview of the research and policy context for the Early Head Start Father Studies. We describe the methods used to conduct the father studies, which began in 1997 and were designed to complement the Early Head Start Research and Evaluation Project, a random assignment evaluation of 3,001 families - half who received Early Head Start services and half who did not. The Early Head Start Father Studies included in the Special Issue addressed 5 key research questions about low-income fathers and their children (all under 3 years old) using a variety of data collection approaches, including mother report, father report, father - child videotaped interactions, and Early Head Start program staff report. Here we describe the father studies' methods and response rates, father demographics, and father - child relationship status. [ABSTRACT FROM AUTHOR]

Objective. To gain a better understanding of how low-income fathers of young children think about their role as fathers, we conducted a qualitative inquiry into the beliefs of fathers of 24-month-old children about what 'good fatherhood' means to them. Design. The 575 open-ended interviews, collected in 14 Early Head Start Fathers of Toddlers Qualitative Interview Substudy sites around the United States were analyzed using NUD*IST qualitative software to code and categorize the various roles fathers identified as important to them and their children. Results. Four broad types of roles were identified: (1) providing a stable environment (e.g., providing a living, 'being there' emotionally and physically), (2) teaching (e.g., giving guidance, exposing their child to the world), (3) physical interaction (e.g., play, caregiving), and (4) emotional support (e.g., providing love, building self-esteem). Conclusion. The beliefs of these men are considered in the context of historical perceptions of fatherhood, as well as their implications for generative theories of fatherhood. Overall, fathers articulated a strong sense of commitment and intentionality in their plans for interactions with their children. Our findings provide opportunities for service providers and policymakers to develop positive strategies to ensure fathers' ability to carry out their intentions. [ABSTRACT FROM AUTHOR]

The effect of frequency variation (chirp) in an electromagnetic (EM) pulse on the pulse interaction with a charged particle and plasma is studied. Various types of chirp and pulse envelopes are considered. In vacuum, a charged particle receives a kick in the polarization direction after interaction with a chirped EM pulse. Interaction of a one-dimensional chirped pulse with uniform plasma is considered. We found that the amplitude of the wake wave generated in plasma by an EM pulse can be significantly higher when the pulse is chirped. [ABSTRACT FROM AUTHOR]

An approach to bolometry has been developed. It is based on the measurements of optical reflectivity change of a thin metal layer deposited on a transparent substrate. The reflectivity change results from the temperature rise due to absorption of energetic particles or x rays. The sensor of the bolometer has no ohmic contact with the measuring unit, making this method well suited for an environment with strong electromagnetic noise interference. The technique was applied to characterize a method for the generation of intense electron beams in a dense gas. Very high efficiency for the e-beam generation (up to 95%) was measured. [ABSTRACT FROM AUTHOR]

Integrated optical signal processors have been identified as a powerful engine for optical processing of microwave signals. They enable wideband and stable signal processing operations on miniaturized chips with ultimate control precision. As a promising application, such processors enables photonic implementations of reconfigurable radio frequency (RF) filters with wide design flexibility, large bandwidth, and high-frequency selectivity. This is a key technology for photonic-assisted RF front ends that opens a path to overcoming the bandwidth limitation of current digital electronics. Here, the recent progress of integrated optical signal processors for implementing such RF filters is reviewed. We highlight the use of a low-loss, high-index-contrast stoichiometric silicon nitride waveguide which promises to serve as a practical material platform for realizing high-performance optical signal processors and points toward photonic RF filters with digital signal processing (DSP)-level flexibility, hundreds-GHz bandwidth, MHz-band frequency selectivity, and full system integration on a chip scale.

The voltage–power characteristics and spatial structure of an RF discharge in the mixtures of CO[sub 2] and N[sub 2] molecular gases with He at total pressures of tens of torr are studied. One-dimensional numerical simulations of an RF discharge are carried out within two approaches: (i) the distribution function and the related kinetic coefficients are assumed to be functions of the local reduced field, and (ii) the kinetic coefficients are functions of the electron mean energy, which is calculated with allowance for both electron heat conduction and diffusion. The latter approach is shown to better describe the existing experimental dependence of the discharge voltage and the phase shift between the discharge current and voltage on the driving power. © 2002 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Examines operant conditioning and memory retrieval in six-month old infants using a memory reactivation paradigm. Subjects; Procedure; Results; Explanation of reactivation paradigm; More.

We describe the wide and rapid wavelength tuning of a continuous-wave master-oscillator power-amplifier system consisting of a semiconductor-amplifier-based oscillator and an ytterbium (Yb)-doped fiber amplifier. The oscillator utilizes an acoustooptic tunable filter and an intracavity etalon to achieve wavelength tuning of 36 nm in 5 ms. The 50-mW output from the master oscillator was amplified to over 9 W in an Yb-doped fiber amplifier [ABSTRACT FROM PUBLISHER]