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When an ultrashort laser pulse is tightly focused to a size approaching its central wavelength, the properties of the focused spot diverge from the diffraction limited case. Here we report on this change in behavior of a tightly focused Petawatt class laser beam by an F/1 off-axis paraboloid (OAP). Considering the effects of residual aberration, the spatial profile of the near field and pointing error, we estimate the deviation in peak intensities of the focused spot from the ideal case. We verify that the estimated peak intensity values are within an acceptable error range of the measured values. With the added uncertainties in target alignment, we extend the estimation to infer on-target peak intensities of $\geq$ 10$^{22}$ W/cm$^{2}$ for a target at the focal plane of this F/1 OAP., 6 pages, 4 figures

Author(s): Lindner, FH; McCary, E; Jiao, X; Ostermayr, TM; Roycroft, R; Tiwari, G; Hegelich, BM; Schreiber, J; Thirolf, PG | Abstract: The fission-fusion reaction mechanism was proposed in order to generate extremely neutron-rich nuclei close to the waiting point N = 126 of the rapid neutron capture nucleosynthesis process (r-process). The production of such isotopes and the measurement of their nuclear properties would fundamentally help to increase the understanding of the nucleosynthesis of the heaviest elements in the Universe. Major prerequisite for the realization of this new reaction scheme is the development of laser-based acceleration of ultra-dense heavy ion bunches in the mass range of A ≈ 200 and above. In this paper, we review the status of laser-driven heavy ion acceleration in the light of the fission-fusion reaction mechanism. We present results from our latest experiment on heavy ion acceleration, including a new milestone with laser-accelerated heavy ion energies exceeding 5 MeV u-1.

Laser-plasma interactions in the novel regime of relativistically induced transparency (RIT) have been harnessed to generate intense ion beams efficiently with average energies exceeding 10 MeV/nucleon (>100 MeV for protons) at “table-top” scales in experiments at the LANL Trident Laser. By further optimization of the laser and target, the RIT regime has been extended into a self-organized plasma mode. This mode yields an ion beam with much narrower energy spread while maintaining high ion energy and conversion efficiency. This mode involves self-generation of persistent high magnetic fields (∼104 T, according to particle-in-cell simulations of the experiments) at the rear-side of the plasma. These magnetic fields trap the laser-heated multi-MeV electrons, which generate a high localized electrostatic field (∼0.1 T V/m). After the laser exits the plasma, this electric field acts on a highly structured ion-beam distribution in phase space to reduce the energy spread, thus separating acceleration and energy-spread reduction. Thus, ion beams with narrow energy peaks at up to 18 MeV/nucleon are generated reproducibly with high efficiency (≈5%). The experimental demonstration has been done with 0.12 PW, high-contrast, 0.6 ps Gaussian 1.053 μm laser pulses irradiating planar foils up to 250 nm thick at 2–8 × 1020 W/cm2. These ion beams with co-propagating electrons have been used on Trident for uniform volumetric isochoric heating to generate and study warm-dense matter at high densities. These beam plasmas have been directed also at a thick Ta disk to generate a directed, intense point-like Bremsstrahlung source of photons peaked at ∼2 MeV and used it for point projection radiography of thick high density objects. In addition, prior work on the intense neutron beam driven by an intense deuterium beam generated in the RIT regime has been extended. Neutron spectral control by means of a flexible converter-disk design has been demonstrated, and the neutron beam has been used for point-projection imaging of thick objects. The plans and prospects for further improvements and applications are also discussed.

Using 2009 data from the U.S. Energy Information Administration, a study of factors that influence broadband adoption is conducted. The data set includes previously studied demographic factors, as well as records associated with the household’s use of computers, television, pay television services, and broadband. Analysis of the data indicate that, when controlling for a number of demographic factors, the purchase of television services is positively correlated with broadband adoption, with consumers who purchase either cable or satellite television service adopting broadband at a higher rate than those who utilize over-the-air television services. The results suggest that consumers who prefer over-the-air television services may face a more substantial hurdle in broadband adoption, one that might be lowered through the availability of affordable stand-alone broadband services.

I. INTRODUCTION The Telecommunications Act of 1996 marked a major legislative effort to change the structure of telecommunications markets in the United States. While the law affected many aspects of the telecommunications industry, the local exchange market, the last bastion of monopoly remaining after the divestiture of AT & T, commanded special attention. The act specified a new regulatory framework for the local exchange market and removed any remaining state-level legal entry barriers (i.e., grants of exclusive franchise). However, recognizing that legal barriers were not the only impediments to the development of local competition, the act went on to specify changes that recognized the likelihood of lingering technological entry barriers and the scale and scope economies that incumbent firms enjoyed. Three paths to entry were encouraged by the act: facilities-based entry, local service resale, and unbundled network elements. To encourage entry possibilities associated with these options, the act mandated interconnection of networks, thus opening the possibility of facilities-based local exchange competition. Under this entry format, new competitive local exchange carriers (CLECs) could construct their own local networks and interconnect with the incumbent local exchange carriers (ILECs), thus gaining the network economies of a large local calling scope. The act did not stop with mandates for interconnection. A wholesale market for the ILECs' services and network technology was also created. CLECs could become resellers of the ILECs' services through the act's local service resale mandate. Alternatively, the act specified that CLECs could utilize parts of the ILECs' network, such as local loops (the wires that connect ILEC customers to the ILEC switching centers, switching, and transport), through provisions which specified the unbundling of ILEC networks. The CLEC could then combine the ILEC technology with its own technology to provide the desired local exchange services. Implementation of the Telecommunications Act under the direction of the Federal Communications Commission (FCC) also resulted in combinations of network elements, now known as UNE-platforms (or UNE-Ps), becoming available to CLECs. The combined platform of elements is much closer to a service in that it bundles most technology needed to provide local exchange service at a much lower price than local service resale. UNE-Ps have been widely adopted by CLECs. (1) While laying out the general framework, many of the details associated with the mandates identified above were not specified by the act. Rather, the FCC and state public utility commissions (PUCs) were charged with the actual stewardship of opening local markets, including developing necessary rules and establishing prices for interconnection, UNEs, and wholesale services. The process of hammering out the details is ongoing because of a series of legal challenges that have wound their way through the courts, with the U.S. Supreme Court having the "last word" on several key issues. However, in spite of these legal delays, the process of competitive entry began in earnest in late 1996 and is continuing through the present period. While ILECs challenged the authority of the FCC to establish rules, the state PUCs, which had the ultimate authority to determine the prices for the components needed by local entrants, oversaw the introduction of competition in the local exchanges in their jurisdictions. The progress of competitive entry under the provisions of the act, the FCC's rules, and the PUCs' general oversight has been mixed. It is noteworthy that the CLEC industry has suffered considerably in the high-technology bust. A Wall Street Journal article, commenting at the height of the CLEC bust, noted "a broad CLEC index,... reached a peak market cap of $242 billion in March of 2000. By last month (May, 2001), the market cap had dropped to $38 billion--an 83% decline. …

African nations face a dual digital divide: First, the majority of the population lacks basic infrastructure for Internet access. Second, low Internet subscription rates characterize those who have the potential for access. Factors hypothesizedto influence Internet subscription among those with the potential for access include: Economic development, international Internet bandwidth, domestic Internet hosts, ISP market structure, the cost of a local telephone call, andwhether English is an official language. Statistical results indicate the strongest influences on subscription are whether English is an official language, monopoly ISP market structure, overall economic development, and the amount of international bandwidth. r 2003 Elsevier Science Ltd. All rights reserved.

Network trouble reports provide a proxy measure of service quality and network reliability. This paper analyzes the in#uence of local competition, state-level regulation, new technologies, automation, and mergers on RBOC reports of network trouble. Service quality discrimination between residential and business customers is also analyzed. Results indicate that (1) service quality discrimination between business and residential customers in response to competition may be occurring, (2) alternative regulation plans have not led to systematic increases in network trouble, and (3) merger and technology have a consistent impact on repeat trouble. ( 2000 Elsevier Science Ltd. All rights reserved.

This paper examines growth in total factor productivity (TFP) before and after the implementation of alternative regulatory schemes for Ameritech operating companies. A model of TFP growth developed by the FCC is used. Results indicate that the introduction of price cap and incentive regulation leads to statistically significant increases in TFP growth. Results indicate that regulators may need to increase current productivity offsets to achieve a more equitable sharing of productivity gains between shareholders and ratepayers.

Chronicles a series of errors in the Telecommunications Act by using a “fairy tale” scenario to aid in explanation of this US 1996 procedure. Addresses local market jurisdiction and dual cost standards. Concludes many of the Act’s goals remain largely unfulfilled as local exchange customers will not see the benefits the Act was hoped to deliver, until technology allows better delivery.

This paper dynamically models an incumbent Local Exchange Carrier's (LEC's) ability to control market entry with a profit squeeze. The model is consistent with the post-Telecommunications Act of 1996 local exchange market. The model shows that an unconstrained incumbent could choose output prices and input costs to discourage an entrant's output-market production. The impact of a regulatory constraint on incumbent behavior is examined. It is concluded that cost-based input prices may lead to little growth in the entrant's self-provision of inputs and that continuing oversight of output and input prices may be necessary.

Market economies rest on a foundation of the private ownership of resources. Certain resources, however, have been managed outside of the market mechanism, even in the United States’ decidedly pro-free-market economy. The management of radio frequencies, or spectrum, is a prime example of government control of a valuable resource. Spectrum management is practiced by governments around the globe, and the experience of the U.S. Federal Communications Commission (FCC) provides a valuable illustration of how management of this resource may be improved through the use of electronic resources.

Cobalt sulfate is a water-soluble cobalt salt with a variety of industrial and agricultural uses. Several cobalt compounds have induced sarcomas at injection sites in animals, and reports have suggested that exposure to cobalt-containing materials may cause lung cancer in humans. The present studies were done because no adequate rodent carcinogenicity studies had been performed with a soluble cobalt salt using a route relevant to occupational exposures. Groups of 50 male and 50 female F344/N rats and B6C3F1 mice were exposed to aerosols containing 0, 0.3, 1.0, or 3.0 mg/m3 cobalt sulfate hexahydrate, 6 h/day, 5 days/week, for 104 weeks. Survival and body weights of exposed rats and mice were generally unaffected by the exposures. In rats, proteinosis, alveolar epithelial metaplasia, granulomatous alveolar inflammation, and interstitial fibrosis were observed in the lung in all exposed groups. Nonneoplastic lesions of the nose and larynx were also attributed to exposure to all concentrations of cobalt sulfate. In 3.0 mg/m3 male rats and in female rats exposed to 1.0 or 3.0 mg/m3, the incidences of alveolar/bronchiolar neoplasms were increased over those in the control groups. Lung tumors occurred with significant positive trends in both sexes. The incidences of adrenal pheochromocytoma in 1.0 mg/m3 male rats and in 3.0 mg/m3 female rats were increased. Nonneoplastic lesions of the respiratory tract were less severe in mice than in rats. In mice, alveolar/bronchiolar neoplasms in 3.0 mg/m3 males and females were greater than those in the controls, and lung tumors occurred with significantly positive trends. Male mice had liver lesions consistent with a Helicobacter hepaticus infection. Incidences of liver hemangiosarcomas were increased in exposed groups of male mice; however, because of the infection, no conclusion could be reached concerning an association between liver hemangiosarcomas and cobalt sulfate. In summary, exposure to cobalt sulfate by inhalation resulted in increased incidence of alveolar/bronchiolar neoplasms and a spectrum of inflammatory, fibrotic, and proliferative lesions in the respiratory tracts of male and female rats and mice. Adrenal pheochromocytomas were increased in female rats, and possibly in male rats.