Detection of X-ray-Emitting Hypernova Remnants in M101

Based on an ultra deep (230 ks) ROSAT HRI imaging of M101, we have detected 5 X-ray sources that coincide spatially with optical emission line features previously classified as supernova remnants in this nearby galaxy. Two of these coincidences (SNR MF83 and NGC5471B) most likely represent the true physical association of X-ray emission with shock-heated interstellar gas. MF83, with a radius of ~ 134 pc, is one of the largest remnants known. NGC5471B, with a radius of 30 pc and a velocity of at least 350 km/s (FWZI), is extremely bright in both radio and optical. The X-ray luminosities of these two shell-like remnants are $\sim 1$ and $3 \times 10^{38} ergs/s$ (0.5-2 keV), about an order of magnitude brighter than the brightest supernova remnants known in our Galaxy and in the Magellanic Clouds. The inferred blastwave energy is $\sim 3 \times 10^{52} ergs$ for NGC5471B and $\sim 3 \times 10^{53}$ ergs for MF83. Therefore, the remnants likely originate in hypernovae, which are a factor of $\gtrsim 10$ more energetic than canonical supernovae and are postulated as being responsible for Gamma-ray bursts observed at cosmological distances. The study of such hypernova remnants in nearby galaxies has the potential to provide important constraints on the progenitor type, rate, energetics, and beaming effect of Gamma-ray bursts.Comment: 10 pages, 2 gif figures, Accepted for publication in Astrophysical Journal Letter

Lattice Boltzmann Magnetohydrodynamics

Lattice gas and lattice Boltzmann methods are recently developed numerical schemes for simulating a variety of physical systems. In this paper a new lattice Boltzmann model for modeling two-dimensional incompressible magnetohydrodynamics (MHD) is presented. The current model fully utilizes the flexibility of the lattice Boltzmann method in comparison with previous lattice gas and lattice Boltzmann MHD models, reducing the number of moving directions from $36$ in other models to $12$ only. To increase computational efficiency, a simple single time relaxation rule is used for collisions, which directly controls the transport coefficients. The bi-directional streaming process of the particle distribution function in this paper is similar to the original model [ H. Chen and W. H. Matthaeus, Phys. Rev. Lett., {\bf 58}, 1845(1987), S.Chen, H.Chen, D.Mart\'{\i}nez and W.H.Matthaeus, Phys. Rev. Lett. {\bf 67},3776 (1991)], but has been greatly simplified, affording simpler implementation of boundary conditions and increasing the feasibility of extension into a workable three-dimensional model. Analytical expressions for the transport coefficients are presented. Also, as example cases, numerical calculation for the Hartmann flow is performed, showing a good agreement between the theoreticalComment: 45 pages, to appear in Physics of Plasma

In Vivo Evolution of Butane Oxidation by Terminal Alkane Hydroxylases AlkB and CYP153A6

Enzymes of the AlkB and CYP153 families catalyze the first step in the catabolism of medium-chain-length alkanes, selective oxidation of the alkane to the 1-alkanol, and enable their host organisms to utilize alkanes as carbon sources. Small, gaseous alkanes, however, are converted to alkanols by evolutionarily unrelated methane monooxygenases. Propane and butane can be oxidized by CYP enzymes engineered in the laboratory, but these produce predominantly the 2-alkanols. Here we report the in vivo-directed evolution of two medium-chain-length terminal alkane hydroxylases, the integral membrane di-iron enzyme AlkB from Pseudomonas putida GPo1 and the class II-type soluble CYP153A6 from Mycobacterium sp. strain HXN-1500, to enhance their activity on small alkanes. We established a P. putida evolution system that enables selection for terminal alkane hydroxylase activity and used it to select propane- and butane-oxidizing enzymes based on enhanced growth complementation of an adapted P. putida GPo12(pGEc47{Delta}B) strain. The resulting enzymes exhibited higher rates of 1-butanol production from butane and maintained their preference for terminal hydroxylation. This in vivo evolution system could be useful for directed evolution of enzymes that function efficiently to hydroxylate small alkanes in engineered hosts

A Critical Examination of Hypernova Remnant Candidates in M101. II. NGC 5471B

NGC 5471B has been suggested to contain a hypernova remnant because of its extraordinarily bright X-ray emission. To assess its true nature, we have obtained high-resolution images in continuum bands and nebular lines with the Hubble Space Telescope, and high-dispersion long-slit spectra with the Kitt Peak National Observatory 4-m echelle spectrograph. The images reveal three supernova remnant (SNR) candidates in the giant HII region NGC 5471, with the brightest one being the 77x60 pc shell in NGC 5471B. The Ha velocity profile of NGC 5471B can be decomposed into a narrow component (FWHM = 41 km/s) from the background HII region and a broad component (FWHM = 148 km/s) from the SNR shell. Using the brightness ratio of the broad to narrow components and the Ha flux measured from the WFPC2 Ha image, we derive an Ha luminosity of (1.4+-0.1)x10^39 ergs/s for the SNR shell. The [SII]6716,6731 doublet ratio of the broad velocity component is used to derive an electron density of ~700 cm^-3 in the SNR shell. The mass of the SNR shell is thus 4600+-500 Mo. With a \~330 km/s expansion velocity implied by the extreme velocity extent of the broad component, the kinetic energy of the SNR shell is determined to be 5x10^51 ergs. This requires an explosion energy greater than 10^52 ergs, which can be provided by one hypernova or multiple supernovae. Comparing to SNRs in nearby active star formation regions, the SNR shell in NGC 5471B appears truly unique and energetic. We conclude that the optical observations support the existence of a hypernova remnant in NGC 5471B.Comment: 27 pages, 9 figures, to appear in May 2002 issue of The Astronomical Journa

Two-dimensional protein crystallization via metal-ion coordination by naturally occurring surface histidines

A powerful and potentially general approach to the targeting and crystallization of proteins on lipid interfaces through coordination of surface histidine residues to lipid-chelated divalent metal ions is presented. This approach, which should be applicable to the crystallization of a wide range of naturally occurring or engineered proteins, is illustrated here by the crystallization of streptavidin on a monolayer of an iminodiacetate-Cu(II) lipid spread at the air-water interface. This method allows control of the protein orientation at interfaces, which is significant for the facile production of highly ordered protein arrays and for electron density mapping in structural analysis of two-dimensional crystals. Binding of native streptavidin to the iminodiacetate-Cu lipids occurs via His-87, located on the protein surface near the biotin binding pocket. The two-dimensional streptavidin crystals show a previously undescribed microscopic shape that differs from that of crystals formed beneath biotinylated lipids

Community Resilience: A Dynamic Model for Public Health 3.0.

OBJECTIVE: To establish a model for Public Health 3.0 in order to define and measure community resilience (CR) as a method to measure equity, address structural racism, and improve population health. DESIGN: To develop the CR model, we conducted a literature review in medicine, psychology, early childhood development, neurobiology, and disaster preparedness and response and applied system dynamics modeling to analyze the complex interactions between public systems, policies, and community. MAIN OUTCOME MEASURES: The CR model focuses on community and population health outcomes associated with the policies and practices of the housing, public education, law enforcement, and criminal justice sectors as CR measures. The model demonstrates how behaviors of these systems interact and produce outcome measures such as employment, homelessness, educational attainment, incarceration, and mental and physical health. RESULTS: The policies and practices within housing, public schools, law enforcement, and criminal justice can suppress resilience for families and communities because they are shaped by structural racism and influence the character and nature of resources that promote optimal community health and well-being. CONCLUSIONS: Community resilience is relational and place-based and varies depending on the demographic makeup of residents, historical patterns of place-based racism and discrimination, jurisdictional policy, and investment priorities-all influenced by structural racism. IMPLICATIONS FOR POLICY AND PRACTICE: Using system dynamics modeling and the CR approach, chief health strategists can convene partners from multiple sectors to systematically identify, measure, and address inequities produced by structural racism that result in and contribute to adverse childhood and community experiences

Taking Gene Therapy into the Clinic

Gene therapy represents a promising novel treatment strategy for colorectal cancer. Preclinical data has been encouraging and several clinical trials are underway. Many phase 1 trials have proven the safety of the reagents but have yet to demonstrate significant therapeutic benefit. Ongoing efforts are being made to improve the efficiency of gene delivery and accuracy of gene targeting with the aim of enhancing antitumor potency. It is envisaged that gene therapy will be used in combination with other therapies including surgery, chemotherapy, and radiotherapy to facilitate the improvements in cancer treatments in the future

Bioelectronic DNA detection of human papillomaviruses using eSensor™: a model system for detection of multiple pathogens

BACKGROUND: We used human papillomaviruses (HPV) as a model system to evaluate the utility of a nucleic acid, hybridization-based bioelectronic DNA detection platform (eSensor™) in identifying multiple pathogens. METHODS: Two chips were spotted with capture probes consisting of DNA oligonucleotide sequences specific for HPV types. Electrically conductive signal probes were synthesized to be complementary to a distinct region of the amplified HPV target DNA. A portion of the HPV L1 region that was amplified by using consensus primers served as target DNA. The amplified target was mixed with a cocktail of signal probes and added to a cartridge containing a DNA chip to allow for hybridization with complementary capture probes. RESULTS: Two bioelectric chips were designed and successfully detected 86% of the HPV types contained in clinical samples. CONCLUSIONS: This model system demonstrates the potential of the eSensor platform for rapid and integrated detection of multiple pathogens