Ionization waves of arbitrary velocity driven by a flying focus

A chirped laser pulse focused by a chromatic lens exhibits a dynamic, or "flying," focus in which the trajectory of the peak intensity decouples from the group velocity. In a medium, the flying focus can trigger an ionization front that follows this trajectory. By adjusting the chirp, the ionization front can be made to travel at an arbitrary velocity along the optical axis. We present analytical calculations and simulations describing the propagation of the flying focus pulse, the self-similar form of its intensity profile, and ionization wave formation. The ability to control the speed of the ionization wave and, in conjunction, mitigate plasma refraction has the potential to advance several laser-based applications, including Raman amplification, photon acceleration, high harmonic generation, and THz generation

Development of improved structural adhesives Annual summary report, 1 Jul. 1967 - 3 Dec. 1968

Improved structural adhesives for bonding aluminum over low temperature

Resonance absorption of a broadband laser pulse

Broad bandwidth, infrared light sources have the potential to revolutionize inertial confinement fusion (ICF) by suppressing laser-plasma instabilities. There is, however, a tradeoff: The broad bandwidth precludes high efficiency conversion to the ultraviolet, where laser-plasma interactions are weaker. Operation in the infrared could intensify the role of resonance absorption, an effect long suspected to be the shortcoming of early ICF experiments. Here we present simulations exploring the effect of bandwidth on resonance absorption. In the linear regime, bandwidth has little effect on resonance absorption; in the nonlinear regime, bandwidth suppresses enhanced absorption resulting from the electromagnetic decay instability. These findings evince that regardless of bandwidth, an ICF implosion will confront at least linear levels of resonance absorption

Mapping of serotype-specific, immunodominant epitopes in the NS-4 region of hepatitis C virus (HCV):use of type-specific peptides to serologically differentiate infections with HCV types 1, 2, and 3

The effect of sequence variability between different types of hepatitis C virus (HCV) on the antigenicity of the NS-4 protein was investigated by epitope mapping and by enzyme-linked immunosorbent assay with branched oligopeptides. Epitope mapping of the region between amino acid residues 1679 and 1768 in the HCV polyprotein revealed two major antigenic regions (1961 to 1708 and 1710 to 1728) that were recognized by antibody elicited upon natural infection of HCV. The antigenic regions were highly variable between variants of HCV, with only 50 to 60% amino acid sequence similarity between types 1, 2, and 3. Although limited serological cross-reactivity between HCV types was detected between peptides, particularly in the first antigenic region of NS-4, type-specific reactivity formed the principal component of the natural humoral immune response to NS-4. Type-specific antibody to particular HCV types was detected in 89% of the samples from anti-HCV-positive blood donors and correlated almost exactly with genotypic analysis of HCV sequences amplified from the samples by polymerase chain reaction. Whereas almost all blood donors appeared to be infected with a single virus type (97%), a higher proportion of samples (40%) from hemophiliacs infected from transfusion of non-heat-inactivated clotting factor contained antibody to two or even all three HCV types, providing evidence that long-term exposure may lead to multiple infection with different variants of HCV

Numerical Simulation of magnetized jet creation using a hollow ring of laser beams

Three dimensional FLASH magneto-hydrodynamics(MHD) modeling is carried out to interpret the OMEGA laser experiments of strongly magnetized, highly collimated jets driven by a ring of 20 OMEGA beams. The predicted optical Thomson scattering spectra and proton images are in good agreement with a subset of the experimental data. Magnetic fields generated via the Biermann battery term are amplified at the boundary between the core and the surrounding of the jet. The simulation predicts multiple axially aligned magnetic flux ropes with alternating poloidal component. Future applications of the hollow ring configuration in laboratory astrophysics are discussed

Phytosanitary irradiation for export of fresh produce: commercial adoption in Hawaii and current issues

Hawaii is a pioneer in the use of phytosanitary irradiation. Irradiation is an approved treatment to control quarantine insect pests in 17 fruits and 7 vegetables for export from Hawaii to the US mainland. The commercial X-ray irradiation facility, Hawaii Pride LLC, has been shipping tropical fruits and vegetables to the US mainland using irradiation since 2000. Hawaiian purple sweet potato is the highest volume product with annual exports of more than 12 million lbs (5,500 tonnes). The advent of generic radiation treatments for tephritid fruit flies (150 Gy) and other insects (400 Gy) has accelerated commodity export approvals and facilitated adoption by foreign trading partners. Current impediments to wider adoption include the labeling requirement, the 1 kGy limit for fresh horticultural products, and non-acceptance of phytosanitary irradiation in Japan and the European Union. USDA Animal and Plant Health Inspection Service (APHIS) has restricted the use of modified atmosphere packaging (MAP) for irradiated fresh fruits exported to the US due to possible increased radiotolerance in the target insects. Data are presented for response of melon fly in papaya to several types of MAP with radiation treatment at 45–65 Gy. Low oxygen atmospheres can increase insect radio-tolerance, but the effect is dependent on oxygen concentration and radiation dose

Phytosanitary irradiation for export of fresh produce: commercial adoption in Hawaii and current issues

Hawaii is a pioneer in the use of phytosanitary irradiation. Irradiation is an approved treatment to control quarantine insect pests in 17 fruits and 7 vegetables for export from Hawaii to the US mainland. The commercial X-ray irradiation facility, Hawaii Pride LLC, has been shipping tropical fruits and vegetables to the US mainland using irradiation since 2000. Hawaiian purple sweet potato is the highest volume product with annual exports of more than 12 million lbs (5,500 tonnes). The advent of generic radiation treatments for tephritid fruit flies (150 Gy) and other insects (400 Gy) has accelerated commodity export approvals and facilitated adoption by foreign trading partners. Current impediments to wider adoption include the labeling requirement, the 1 kGy limit for fresh horticultural products, and non-acceptance of phytosanitary irradiation in Japan and the European Union. USDA Animal and Plant Health Inspection Service (APHIS) has restricted the use of modified atmosphere packaging (MAP) for irradiated fresh fruits exported to the US due to possible increased radiotolerance in the target insects. Data are presented for response of melon fly in papaya to several types of MAP with radiation treatment at 45–65 Gy. Low oxygen atmospheres can increase insect radio-tolerance, but the effect is dependent on oxygen concentration and radiation dose

The Making of the Clean Air Act

The 1970 Clean Air Act is arguably Congress’ most important environmental enactment. Since it became law fifty years ago, much could be and has been said about how it has changed both the physical environment and the contours of environmental law. Much less, however, has been written on the genesis of the Act itself. Where its history is discussed, it is often segmented or heavily summarized. In this Article, we take on the story of how the Act came to be as well as how early enforcement practices cemented its importance in the legal landscape. To do so, we rely upon an unprecedented analysis and synthesis of previously underexplored strands of the story, incorporating many unmined sources and original research. This story weaves together the contributions of officials and staff in the Nixon Administration, Congress, and the judiciary to provide what is hoped to be an integrated, meaningful, and readable account of the making of the Clean Air Act

Reconsidering NEPA

The National Environmental Policy Act (NEPA) ushered in the modern era of environmental law. Thanks to its environmental impact statement (EIS) provision, it remains, by far, the most litigated environmental statute. Many administrations have sought to weaken the law. The Trump administration, for example, put into place regulations that strictly limit the EIS process, which the Biden administration seems poised to roll back. For the most part, however, NEPA has shown remarkable staying power and resilience since its passage just over fifty years ago. As a result, its legislative history remains relevant. But the accepted history of NEPA is deeply flawed. By bringing the history to light, this Article makes three contributions. First, relying on both original primary sources and a thorough review of the literature, we provide a nuanced and engaging history of the EIS provision, correcting common misconceptions of the accepted story. Second, we show why understanding this more accurate history of the Act’s key provision can rebut major threats to NEPA and the regulations that govern it, such as those introduced during the Trump administration. Third, our granular history of NEPA provides an ideal experiment to test the accuracy of traditional canons of legislative history. We find that most canons fail to recognize the most critical aspects of NEPA’s history. Positive political theory–derived canons, on the other hand, most accurately capture the actual legislative history