Integrated simulation results of femtosecond laser ablation of copper were compared with new experimental data. The numerical analysis was performed using our newly developed FEMTO-2D computer package based on the solution of the two-temperature model. Thermal dependence of target optical and thermodynamic processes was carefully considered. The experimental work was conducted with our 40 fs 800 nm Ti:sapphire laser in the energy range from 0.14 mJ to 0.77 mJ. Comparison of measured ablation profiles with simulation predictions based on phase explosion criterion has demonstrated that more than one ablation mechanisms contribute to the total material removal even in the laser intensity range where explosive boiling is dominating. Good correlation between experimental and simulation results was observed for skin depth and hot electron diffusion depth – two parameters commonly considered to identify two ablation regimes in metal. Analysis of the development dynamics for electron–lattice coupling and electron thermal conduction allowed explaining different ablation regimes because of the interplay of the two parameters.

A vast amount of agricultural land in the USA will change hands in the coming years as established farmers age and transition out of farm ownership. As a result, beginning farmers are likely to continue to face numerous obstacles as they try to find and purchase the property. Two of the greatest barriers include the high price that farm property usually commands and the steady conversion of farmland to non-agricultural uses (e.g., suburban development). Non-profit organizations and government agencies have used conservation easements extensively to protect against conversion of agricultural land, but, too often, that does not ensure affordability for beginning farmers. Accordingly, advocates have developed supplemental land transfer tools intended to enhance conservation easements and help beginning farmers gain access to land. In this exploratory research, we look at two of these novel tools, namely Conservation Buyer Programs (CBPs) and the option to purchase at agricultural value (OPAV). Specifically, we present case studies about two entities that use OPAV and two that use CBPs in order to understand how these tools function and whether they improve land access for beginning farmers. Interviews with professionals and beginning farmers who have worked with these tools in four states inform our analysis and add depth to previous scholarship. We found that OPAV and CBPs can improve access to agricultural land for beginning farmers under certain circumstances. These tools, however, are not panaceas to the challenge land affordability presents, nor are they the only tools used by the entities we studied. CBPs alone have rarely been used to help new farmers; yet, they have been paired effectively with a conservation easement and OPAV. Additionally, we found a similar tool, the simultaneous sale, has been quite effective when paired with OPAV, and less costly than the traditional conservation buyer approach. All of these tools expand the land access toolbox in important ways, but given the paucity of existing scholarship on this topic, additional research is needed. Practitioners and researchers must think critically about whether these tools are the most effective instruments to employ in the effort to get beginning farmers on the land.

The interaction of femtosecond laser with initially cold solid metallic targets (Al, Au, Cu, Mo, Ni) was investigated in a wide range of laser intensity with focus on the laser energy absorption efficiency. Our developed simulation code (FEMTO-2D) is based on two-temperature model in two-dimensional configuration, where the temperature-dependent optical and thermodynamic properties of the target material were considered. The role of the collisional processes in the ultrashort pulse laser–matter interaction has been carefully analyzed throughout the process of material transition from the cold solid state into the dense plasma state during the pulse. We have compared the simulation predictions of the laser pulse absorption with temperature-dependent reflectivity and optical penetration depth to the case of constant optical parameters. By considering the effect of the temporal and spatial (radial) distribution of the laser intensity on the light absorption efficiency, we obtained a good agreement between the simulated results and available experimental data. The appropriate model for temperature-dependent optical parameters defining the laser absorption efficiency will allow more accurate simulation of the target thermal response in the applications where it is critical, such as prediction of the material damage threshold, laser ablation threshold, and the ablation profile.

The response of ‘Era’ (tolerant) and ‘Coteau’ (susceptible) hard red spring wheat (Triticum aestivum L.) to CGA-82725 2-propynyl ester of {2-[4- [(3,5-dichloro-2-pyridinyl)oxy] phenoxy] propanoic acid} was determined in field and greenhouse evaluations. Era wheat was most susceptible to CGA-82725 applied at early jointing through the boot stage. Coteau wheat was most susceptible at die two-leaf stage and between early jointing through spike emergence. Coteau was injured more than Era wheat as the CGA-82725 rate was increased from 0.14 to 0.28 kg ai/ha. Wheat grain yield reductions were greatest when CGA-82725 was applied at the early jointing through boot stage for both cultivars and averaged 73% of the control. Absorption and translocation of 14C-CGA-82725 were similar and increased over time regardless of cultivar. Most of the absorbed 14C remained in the treated leaf in both cultivars.

We developed a comprehensive model for simulating laser/target interaction in the presence of external axial magnetic fields. The model was integrated into the framework of the HEIGHTS-LPP computer simulation package and benchmarked with recent experimental results. The package was then used to study the angular distribution of extreme ultraviolet (EUV) photon output in plasmas produced in tin planar targets by a Nd:YAG laser. A moderate (0.5 T) permanent magnetic field does not affect EUV source evolution and output. More effective control of plasma plume expansion should be based on magnetic field gradients, that is, on the temporary varying magnetic fields as a magnetic pinch. Analysis of angular EUV output showed strong anisotropy of photon emissions. We found that the correct monitoring angle (i.e., at which the measured EUV flux corresponds to the averaged value after the correctly integrated angular distribution) does not depend on laser irradiance in the studied range and is equivalent to ~60°. We recommend arranging the EUV sensors accordingly in experiments with planar tin targets.

Models and experiments were developed to study femtosecond laser ablation of silicon using 800 nm, 40 fs pulses with fluences ranging from 0.5 to 35 J/cm2. At low fluences, ablation was found to occur due to bubble formation and splashing within the melt layer. At higher fluences, it was found that the ablation depth exceeded the melt layer depth due to shockwave ablation. The variation in ion flux and ion velocity was also studied both experimentally and theoretically. It was found that the variation in ion flux is mainly dependent on the variation in the average charge state, with only a small variation in the total number of ions above $\sim \!\!1.5\; \,{\rm J/c}{{\rm m}^2}$. Comparisons between the theoretical and experimental ion flux showed that higher charge state ions received greater portion of the laser energy compared with lower charge state ions.

We investigated the expansion dynamics of laser-produced plasmas expanding into an axial magnetic field. Plasmas were generated by focusing 1.064 μm Nd:YAG laser pulses onto a planar tin target in vacuum and allowed to expand into a 0.5 T magnetic field where the field lines were aligned along the plume expansion direction. Gated images employing an intensified charge-coupled device showed focusing of the plasma plume, which were also compared with results, obtained using particle-in-cell modeling methods. The estimated density and temperature of the plasma plumes employing emission spectroscopy revealed significant changes in the presence and absence of the 0.5 T magnetic field. In the presence of the field, the electron temperature is increased with distance from the target, while the density showed opposite effects.

Laser ablation of graphite materials in the presence of an external magnetic field is studied with the use of the newly developed HEIGHTS-PIC particle-in-cell code and compared with both theoretical and experimental results. Carbon plumes behavior controlled by a strong magnetic field is of interest to evaluate the plume shielding effects to protect the original exposed target from further damage and erosion. Since intense power deposition on plasma facing components is expected during Tokamaks loss of plasma confinement events such as disruptions, vertical displacements event, runaway electrons, or during normal operating conditions such as edge-localized modes, it is critical to better understand the evolving target plasma behavior for more accurate prediction of the potential damage created by these high-energetic dumps which may not be easily mitigated without loss of structural and functional performance of the plasma facing components. Numerical experiments have been performed to provide benchmarking conditions for the HEIGHTS-PIC simulation package originally designed to evaluate the erosion of the Tokamak surfaces, splashing of the melted/ablated-vaporized material, and transport into the bulk plasma with consequent plasma contamination. Evolving target plasma temperature and density are calculated and compared with measured reported values available into literature for similar conditions and show good agreement with the HEIGHTS-PIC package predictions.

Large energy fluxes and energy deposition are often found during off normal events in fusion reactors both magnetic and inertial confinement. Great temperature excursions can be found in the plasma facing components materials resulting in melting, evaporation, and expansion of the target material vapor cloud and successive plasma interaction. A general methodology for the computational solution of this very complex problem is proposed in this paper using a novel approach of the Particle-in-Cell method. This novel approach preserves many of the original Particle-in-Cell methodology proposed by Harlow's but introduces several changes to the method, which makes it particularly suitable in plasma dynamics applications as Tokamaks devices. Benchmarking is done using results from the very well-known and benchmarked HEIGHTS computer package and using available results from the MK200 plasma gun experiments. The general scheme is explained in detail and results and discussion related to the main computational aspects are presented. In particular, the critical importance of the starting computational mesh versus the aimed accuracy is studied and explained. The methodology is different from any other presented in literature because the dynamics of the physical problem dictates that as enough energy is being dumped on the target plate, melting and evaporation of the material takes place. As time progresses, new sample particles are introduced in the system making this boundary a dynamic one along time. Computer time is discussed in relation to the initial sample particle loading, aimed accuracy and importance of the time used for solving the radiation transport at each time step.

Non-equilibrium heat transfer described by a two-step temperature model was developed to study the thermal evolution through target materials irradiated by femtosecond laser pulse. Two-dimensional heat transfer equations were solved numerically. The temperature dependent thermo-physical properties of the electron and the lattice are considered in the model. The Gaussian spatial and temporal distribution of the heat and temperature of the electron and the lattice is presented. The effect of reflectivity, electron — lattice coupling factor, and the spot size was studied using copper targets.

Laser-produced plasma (LPP) devices are being developed as a light source for the extreme ultraviolet (EUV) lithography applications. One concern of such devices is to increase the conversion efficiency of laser energy to EUV light. A new idea based on the initiation and confinement of cumulative plasma jet inside a hollow laser beam is developed and simulated. The integrated computer model (HEIGHTS) was used to simulate the plasma behavior and the EUV radiation output in the LPP devices. The model takes into account plasma heat conduction and magnetohydrodynamic processes in a two-temperature approximation, as well as detailed photon radiation transport in 3D Monte Carlo model. The model employs cylindrical 2D version of a total variation-diminishing scheme (for the plasma hydrodynamics) and an implicit scheme with the sparse matrix linear solver (to describe heat conduction). Numerical simulations showed that the EUV efficiency of the proposed hollow-beam LPP device to be higher than the current standard devices.

Treatment with interferon-alpha (IFN-α) has been shown to adversely affect cognitive functioning in patients with a variety of medical disorders, but information about the effects of IFN-α on cognitive functioning in patients with chronic hepatitis C (CHC) is limited. The purpose of this study was to examine the effects of IFN-α on neuropsychological test performance in CHC patients. Participants were 30 patients with CHC, 11 who underwent IFN-α therapy and 19 who did not. All participants were tested at baseline (i.e., pretreatment) and approximately 6 months later with the Symbol Digit Modalities Test and Trail Making Test. Results revealed that the treatment group performed significantly worse than untreated CHC patients on Part B of the Trail Making Test after approximately 6 months of treatment. No significant group differences were found on Part A of the Trail Making Test or Symbol Digit Modalities Test. Findings suggest that CHC patients undergoing treatment with IFN-α may experience reduced abilities to benefit from practice but suffer no decrements in performance after 6 months of treatment. Additional research is needed to replicate these findings and to explore risk factors for susceptibility to IFN-α-induced effects. (JINS, 2005, 11, 16–22.)

Generation of extreme ultraviolet (EUV) light for nanolithography requires the use of hot, dense plasmas. Gas discharge produced plasma (GDPP) and laser produced plasma (LPP) are the primary configurations used to generate these plasmas. Both GDPP and LPP collector mirror systems face serious issues regarding lifetime and EUV light reflectivity performance. For both configurations debris, fast ions, fast neutrals, and condensable EUV radiator fuels (Li, Sn) interact with nearby collector mirrors. Sn, in particular is used due to its high conversion efficiency in the 13.5-nm in-band spectrum. In addition to debris, collector mirrors are exposed to impurities (H,C,O,N), off-band radiation (depositing heat) and highly-charged ions leading to their degradation and consequently limiting 13.5 nm light reflection intensity.

This work presents results of Ru and Rh-based collector optics irradiated by Sn ions between at 1.3 keV and exposed to Sn thermal atoms at room temperature. In-situ metrology monitors the effects of ion implantation on ion-induced erosion and EUV reflectivity changes using low-energy ion scattering spectroscopy and X-ray photoelectron spectroscopy. Results find that Sn implants at the first few monolayers leading to a mixed layer at the surface. Sn thermal atoms deposit on top of the mirror surface leading to 10-20% loss of collector mirror EUV light reflectivity.

Hepatitis C virus (HCV) infection is a major public-health-care problem, with over 170 million infected worldwide. Patients with chronic HCV infection often complain of various cognitive problems as well as symptoms of depression, anxiety, and fatigue. Relatively little is known, however, about the specific cognitive deficits that are common among HCV patients, and the influence of psychiatric symptomatology on cognitive functioning. In the current study of 21 chronically infected HCV patients, we assessed subjective cognitive dysfunction, depression, anxiety, and fatigue and compared these symptom areas to cognitive tests assessing visuoconstruction, learning, memory, visual attention, psychomotor speed, and mental flexibility. Results revealed that cognitive impairment ranged from 9% of patients on a visuoconstruction task to 38% of patients on a measure of complex attention, visual scanning and tracking, and psychomotor speed, and greater HCV disease severity as indicated by liver fibrosis was associated with greater cognitive dysfunction. Objective cognitive impairment was not related to subjective cognitive complaints or psychiatric symptomatology. These findings suggest that a significant portion of patients with chronic HCV experience cognitive difficulties that may interfere with activities of daily living and quality of life. Future research using cognitive measures with HCV-infected patients may assist researchers in identifying if there is a direct effect of HCV infection on the brain and which patients may be more likely to progress to cirrhosis and hepatic encephalopathy. (JINS, 2003, 9, 847–854.)

Significant interest has recently focused on the use of liquid-metal targets flowing with high velocities for various high-power nuclear and high-energy physics applications such as fusion reactor first-walls, the Spallation Neutron Source, Isotope Separation On Line, and Muon Collider projects. This is because the heat generated in solid targets due to beam or plasma bombardment cannot be removed easily and the resulting thermal shock damage could be a serious lifetime problem for long-term operation. More recently, the use of free or open flying-liquid jets has been proposed for higher-power-density applications. The behavior of a free-moving liquid mercury or gallium jet subjected to proton beam deposition in a strong magnetic field has been modeled and analyzed for the Muon Collider project. Free-liquid-metal jets can offer significant advantages over conventional solid targets, particularly for the more demanding and challenging high-power applications. However, the use of free-moving liquid-metal targets raises a number of new and challenging problems such as instabilities of the jet in a strong magnetic field, induced eddy-current effects on jet shape, thermal-shock formation, and possible jet fragmentation. Problems associated with shock heating of liquid jets in a strong magnetic field are analyzed in this study.

The structure of a collisionless scrape-off-layer (SOL) plasma in tokamak reactors is studied in order to define the electron distribution function and the corresponding sheath potential between the divertor plate and the edge plasma. The collisionless model is shown to be valid during the thermal phase of plasma disruption, as well as during the newly desired low-recycling normal phase of operation with low-density, high-temperature, edge plasma conditions. An analytical solution is developed by solving the Fokker–Planck equation for electron distribution and balance in the SOL. The solution is in good agreement with numerical studies using Monte Carlo methods. The analytical solutions provide insight into the role of different physical and geometrical processes in a collisionless SOL during disruptions and during the enhanced phase of normal operation over a wide range of parameters.

Since recent reports suggest structural brain abnormalities in autistic patients, we analysed magnetic resonance imaging (MAI) scans of autistic children. Planimetric measurements were done on midsagittal MRI scans, produced with a 0.5 T superconducting magnet. Scans of 13 ‘high-level’ austic subjects were compared with 35 control MRI scans, read as anatomically normal by a neuroradiologist. Corpus callosal, fourth ventricular, cerebellar, cerebral, and cranial areas were measured. The fourth ventricle was found to be significantly larger in the autistic group. No other areas in the midsagittal scans differed statistically between groups. Results suggest that structures defining the fourth ventricle are anatomically altered in autistic patients.