Telemetric Blood Pressure Assessment in Angiotensin II-Infused ApoE\u3csup\u3e-/-\u3c/sup\u3e Mice: 28 Day Natural History and Comparison to Tail-Cuff Measurements

Abdominal aortic aneurysm (AAA) is a disease of the aortic wall, which can progress to catastrophic rupture. Assessment of mechanical characteristics of AAA, such as aortic distensibility, may provide important insights to help identify at-risk patients and understand disease progression. While the majority of studies on this topic have focused on retrospective patient data, recent studies have used mouse models of AAA to prospectively evaluate the evolution of aortic mechanics. Quantification of aortic distensibility requires accurate measurement of arterial blood pressure, particularly pulse pressure, which is challenging to perform accurately in murine models. We hypothesized that volume/pressure tail-cuff measurements of arterial pulse pressure in anesthetized mice would have sufficient accuracy to enable calculations of aortic distensibility with minimal error. Telemetry devices and osmotic mini-pumps filled with saline or angiotensin-II were surgically implanted in male apolipoprotein-E deficient (ApoE-/-) mice. Blood pressure in the aortic arch was measured continuously via telemetry. In addition, simultaneous blood pressure measurements with a volume/pressure tail-cuff system were performed under anesthesia at specific intervals to assess agreement between techniques. Compared to controls, mice infused with angiotensin-II had an overall statistically significant increase in systolic pressure, with no overall difference in pulse pressure; however, pulse pressure did increase significantly with time. Systolic measurements agreed well between telemetry and tail-cuff (coefficient of variation = 10%), but agreement of pulse pressure was weak (20%). In fact, group-averaged pulse pressure from telemetry was a better predictor of a subject\u27s pulse pressure on a given day than a simultaneous tail-cuff measurement. Furthermore, these approximations introduced acceptable errors (15.1 ± 12.8%) into the calculation of aortic distensibility. Contrary to our hypothesis, we conclude that tail-cuff measures of arterial pulse pressure have limited accuracy. Future studies of aneurysm mechanics using the ApoE-/-/angiotensin-II model would be better in assuming pulse pressure profiles consistent with our telemetry findings instead of attempting to measure pulse pressure in individual mice

Very-high-energy gamma radiation associated with the unshocked wind of the Crab pulsar

We show that the relativistic wind in the Crab pulsar, which is commonly thought to be invisible in the region upstream of the termination shock at R < 0.1 pc, in fact could be directly observed through its inverse Compton gamm-ray emission. The search for such specific component of radiation in the gamma-ray spectrum of the Crab can provide unique information about the unshocked pulsar wind that is not accessible at other wavelengths.Comment: 11 pages, 11 figures, to appear in one of the April issues of MNRA

DWPF MATERIALS EVALUATION SUMMARY REPORT

To better ensure the reliability of the Defense Waste Processing Facility (DWPF) remote canyon process equipment, a materials evaluation program was performed as part of the overall startup test program. Specific test programs included FA-04 ('Process Vessels Erosion/Corrosion Studies') and FA-05 (melter inspection). At the conclusion of field testing, Test Results Reports were issued to cover the various test phases. While these reports completed the startup test requirements, DWPF-Engineering agreed to compile a more detailed report which would include essentially all of the materials testing programs performed at DWPF. The scope of the materials evaouation programs included selected equipment from the Salt Process Cell (SPC), Chemical Process Cell (CPC), Melt Cell, Canister Decon Cell (CDC), and supporting facilities. The program consisted of performing pre-service baseline inspections (work completed in 1992) and follow-up inspections after completion of the DWPF cold chemical runs. Process equipment inspected included: process vessels, pumps, agitators, coils, jumpers, and melter top head components. Various NDE (non-destructive examination) techniques were used during the inspection program, including: ultrasonic testing (UT), visual (direct or video probe), radiography, penetrant testing (PT), and dimensional analyses. Finally, coupon racks were placed in selected tanks in 1992 for subsequent removal and corrosion evaluation after chemical runs

Unstable states in QED of strong magnetic fields

We question the use of stable asymptotic scattering states in QED of strong magnetic fields. To correctly describe excited Landau states and photons above the pair creation threshold the asymptotic fields are chosen as generalized Licht fields. In this way the off-shell behavior of unstable particles is automatically taken into account, and the resonant divergences that occur in scattering cross sections in the presence of a strong external magnetic field are avoided. While in a limiting case the conventional electron propagator with Breit-Wigner form is obtained, in this formalism it is also possible to calculate $S$-matrix elements with external unstable particles.Comment: Revtex, 7 pages. To appear in Phys. Rev. D53(2

Resonant Cyclotron Radiation Transfer Model Fits to Spectra from Gamma-Ray Burst GRB870303

We demonstrate that models of resonant cyclotron radiation transfer in a strong field (i.e. cyclotron scattering) can account for spectral lines seen at two epochs, denoted S1 and S2, in the Ginga data for GRB870303. Using a generalized version of the Monte Carlo code of Wang et al. (1988,1989b), we model line formation by injecting continuum photons into a static plane-parallel slab of electrons threaded by a strong neutron star magnetic field (~ 10^12 G) which may be oriented at an arbitrary angle relative to the slab normal. We examine two source geometries, which we denote "1-0" and "1-1," with the numbers representing the relative electron column densities above and below the continuum photon source plane. We compare azimuthally symmetric models, i.e. models in which the magnetic field is parallel to the slab normal, with models having more general magnetic field orientations. If the bursting source has a simple dipole field, these two model classes represent line formation at the magnetic pole, or elsewhere on the stellar surface. We find that the data of S1 and S2, considered individually, are consistent with both geometries, and with all magnetic field orientations, with the exception that the S1 data clearly favor line formation away from a polar cap in the 1-1 geometry, with the best-fit model placing the line-forming region at the magnetic equator. Within both geometries, fits to the combined (S1+S2) data marginally favor models which feature equatorial line formation, and in which the observer's orientation with respect to the slab changes between the two epochs. We interpret this change as being due to neutron star rotation, and we place limits on the rotation period.Comment: LaTeX2e (aastex.cls included); 45 pages text, 17 figures (on 21 pages); accepted by ApJ (to be published 1 Nov 1999, v. 525

The Crab Nebula: interpretation of CHANDRA observations

We interpret the observed X-ray morphology of the central part of the Crab Nebula (torus + jets) in terms of the standard theory by Kennel and Coroniti (1984). The only new element is the inclusion of anisotropy in the energy flux from the pulsar in the theory. In the standard theory of relativistic winds, the Lorentz factor of the particles in front of the shock that terminates the pulsar relativistic wind depends on the polar angle as $\gamma=\gamma_0+\gamma_m\sin^2\theta$, where $\gamma_0 \sim 200$ and $\gamma_m \sim 4.5\times 10^6$. The plasma flow in the wind is isotropic. After the passage of the pulsar wind through the shock, the flow becomes subsonic with a roughly constant (over the plerion volume) pressure $P={1\over 3}n\epsilon$, where $n$ is the plasma particle density and $\epsilon$ is the mean particle energy. Since $\epsilon \sim \gamma mc^2$, a low-density region filled with the most energetic electrons is formed near the equator. A bright torus of synchrotron radiation develops here. Jet-like regions are formed along the pulsar rotation axis, where the particle density is almost four orders of magnitude higher than that in the equatorial plane, because the particle energy there is four orders of magnitude lower. The energy of these particles is too low to produce detectable synchrotron radiation. However, these quasi-jets become comparable in brightness to the torus if additional particle acceleration takes place in the plerion. We also present the results of our study of the hydrodynamic interaction between an anisotropic wind and the interstellar medium. We compare the calculated and observed distributions of the volume intensity of X-ray radiation.Comment: 38 pages, 5 figures. To be published in Astronomy Letters, 2002, N 6, p.

HTS current lead using a composite heat pipe

This paper discusses the design and fabrication of HTS current leads being built by Los Alamos to supply power to a demonstration HTS coil which will operate in a vacuum cooled by a cryocooler. Because vapor cooling is not an option for this application the leads must be entirely conductively cooled. In the design of HTS current leads for this type of application, it is desirable to intercept part of the heat load at an intermediate temperature. This thermal intercept or connection must be electrically insulating but thermally conductive, two mutually exclusive properties of most candidate solid materials. To achieve this end we incorporate a composite nitrogen heat pipe, constructed of conducting and non-conducting materials, to provide efficient thermal communication and simultaneously, electrical isolation between the lead and the intermediate temperature heat sink. Another important feature of the current lead design is the use of high Jc thick film superconductors deposited on a non-conducting substrate to reduce the conductive heat leak through the lower portion of the lead. Two flexible electrical conductors are incorporated to accommodate handling, assembly and the dissimilar expansion coefficients of the various materials

Magnetic Photon Splitting: the S-Matrix Formulation in the Landau Representation

Calculations of reaction rates for the third-order QED process of photon splitting in strong magnetic fields traditionally have employed either the effective Lagrangian method or variants of Schwinger's proper-time technique. Recently, Mentzel, Berg and Wunner (1994) presented an alternative derivation via an S-matrix formulation in the Landau representation. Advantages of such a formulation include the ability to compute rates near pair resonances above pair threshold. This paper presents new developments of the Landau representation formalism as applied to photon splitting, providing significant advances beyond the work of Mentzel et al. by summing over the spin quantum numbers of the electron propagators, and analytically integrating over the component of momentum of the intermediate states that is parallel to field. The ensuing tractable expressions for the scattering amplitudes are satisfyingly compact, and of an appearance familiar to S-matrix theory applications. Such developments can facilitate numerical computations of splitting considerably both below and above pair threshold. Specializations to two regimes of interest are obtained, namely the limit of highly supercritical fields and the domain where photon energies are far inferior to that for the threshold of single-photon pair creation. In particular, for the first time the low-frequency amplitudes are simply expressed in terms of the Gamma function, its integral and its derivatives. In addition, the equivalence of the asymptotic forms in these two domains to extant results from effective Lagrangian/proper-time formulations is demonstrated.Comment: 19 pages, 3 figures, REVTeX; accepted for publication in Phys. Rev.