Two-component radiation model of the sonoluminescing bubble

Based on the experimental data from Weninger, Putterman & Barber, Phys. Rev. (E), 54, R2205 (1996), we offer an alternative interpretation of their experimetal results. A model of sonoluminescing bubble which proposes that the electromagnetic radiation originates from two sources: the isotropic black body or bramsstrahlung emitting core and dipole radiation-emitting shell of accelerated electrons driven by the liquid-bubble interface is outlined.Comment: 5 pages Revtex, submitted to Phys. Rev.

A modified delphi involving laboratory faculty to define essential skills for pharmacy graduates

Objective. To define essential skills for Doctor of Pharmacy (PharmD) graduates that are needed in the four most common sectors of pharmacy practice as determined by expert faculty who instruct within pharmacy skills laboratories. Methods. A three-round Delphi method was used to establish consensus. In the first round, participants were asked what skills were needed by students at entry to practice in community, health-system, ambulatory care, and managed care pharmacy settings. In rounds two and three, participants were asked to rate each skill with a level of importance using a 10-point Likert scale (1=not important to 10=very important). Results. In round one, participants produced a collective list of 289 essential skills. These skill state-ments were sent to participants in rounds two and three to assign a level of importance. After the third round, participants reached consensus using a mean level of importance for a final list of 69 community pharmacy skills, 47 health-system, 60 ambulatory care, and 15 managed care skills. These skills were then mapped to entrustable professional activities domains for schools and colleges pharmacy to use as a resource when assessing core competency development in the curriculum. Conclusion. The Delphi technique was used successfully with expert pharmacy skills laboratory faculty to identify laboratory-focused essential skills that recent PharmD graduates should have prior to entering community, health-system, ambulatory care, or managed care pharmacy practice. These essential skills can be used to guide curriculum development, develop milestone markers, and help ensure students are practice ready

Dynamical Casimir effect for a massless scalar field between two concentric spherical shells

In this work we consider the dynamical Casimir effect for a massless scalar field -- under Dirichlet boundary conditions -- between two concentric spherical shells. We obtain a general expression for the average number of particle creation, for an arbitrary law of radial motion of the spherical shells, using two distinct methods: by computing the density operator of the system and by calculating the Bogoliubov coefficients. We apply our general expression to breathing modes: when only one of the shells oscillates and when both shells oscillate in or out of phase. We also analyze the number of particle production and compare it with the results for the case of plane geometry.Comment: Final version. To apear in Physical Review

Water quality in the central Nebraska basins, Nebraska, 1992-95

This report is intended to summarize major findings that emerged between 1992 and 1995 from the water-quality assessment of the Central Nebraska Basins Study Unit and to relate these findings to water-quality issues of regional and national concern. The information is primarily intended for those who are involved in waterresource management. Indeed, this report addresses many of the concerns raised by regulators, water-utility managers, industry representatives, and other scientists, engineers, public officials, and members of stakeholder groups who provided advice and input to the USGS during this NAWQA Study-Unit investigation. Yet, the information contained here may also interest those who simply wish to know more about the quality of water in the rivers and aquifers in the area where they live. Land use in central Nebraska appears to affect water quality significantly; streams in rangelands generally had fewer occurrences and smaller concentrations of pesticides than did streams in croplands where corn and soybeans were planted extensively. Subbasins with greater proportions of rangeland, such as the Dismal River, had negligible herbicide concentrations. The largest pesticide concentrations were in storm runoff following pesticide applications. Because some pesticide concentrations may exceed the U.S. Environmental Protection Agency’s (USEPA) drinking-water Maximum Contaminant Levels (MCLs) in storm runoff, the timing and intensity of rainfall has implications for drinking-water supplies. Pesticides in streams from storm runoff may enter alluvial aquifers as a consequence of ground-water withdrawals. Sites with degraded water chemistry commonly had degraded physical habitats as well. Streamflow regulation of the Platte River has affected water quality through habitat alterations that are deleterious to native species. The combination of degraded physical and chemical environments commonly resulted in structurally simple fish communities. CONTENTS National Water-Quality Assessment Program .. 1 Summary of major issues and findings... 2 Environmental setting and hydrologic conditions.... 4 Major issues and findings ... 6 Nitrate content in water is related to agricultural land management 6 Agricultural activities potentially affect the management of public water supplies . 8 Water quality in the Platte River alluvial aquifer may be affected by surface-water quality in areas of ground-water withdrawals .. 10 Aquatic environments potentially are altered by human activities... 12 Aquatic and migratory species are affected directly by changes in the physical characteristics of the Platte River .. 14 Water-quality conditions in anational context ... 16 Study design and data collection .. 20 Summary of compound detections and concentrations ... 22 References . 28 Glossary 3

Mechanisms for Stable Sonoluminescence

A gas bubble trapped in water by an oscillating acoustic field is expected to either shrink or grow on a diffusive timescale, depending on the forcing strength and the bubble size. At high ambient gas concentration this has long been observed in experiments. However, recent sonoluminescence experiments show that in certain circumstances when the ambient gas concentration is low the bubble can be stable for days. This paper presents mechanisms leading to stability which predict parameter dependences in agreement with the sonoluminescence experiments.Comment: 4 pages, 3 figures on request (2 as .ps files

Competing Ultrafast Energy Relaxation Pathways in Photoexcited Graphene

For most optoelectronic applications of graphene a thorough understanding of the processes that govern energy relaxation of photoexcited carriers is essential. The ultrafast energy relaxation in graphene occurs through two competing pathways: carrier-carrier scattering -- creating an elevated carrier temperature -- and optical phonon emission. At present, it is not clear what determines the dominating relaxation pathway. Here we reach a unifying picture of the ultrafast energy relaxation by investigating the terahertz photoconductivity, while varying the Fermi energy, photon energy, and fluence over a wide range. We find that sufficiently low fluence ($\lesssim$ 4 $\mu$J/cm$^2$) in conjunction with sufficiently high Fermi energy ($\gtrsim$ 0.1 eV) gives rise to energy relaxation that is dominated by carrier-carrier scattering, which leads to efficient carrier heating. Upon increasing the fluence or decreasing the Fermi energy, the carrier heating efficiency decreases, presumably due to energy relaxation that becomes increasingly dominated by phonon emission. Carrier heating through carrier-carrier scattering accounts for the negative photoconductivity for doped graphene observed at terahertz frequencies. We present a simple model that reproduces the data for a wide range of Fermi levels and excitation energies, and allows us to qualitatively assess how the branching ratio between the two distinct relaxation pathways depends on excitation fluence and Fermi energy.Comment: Nano Letters 201