Improved Blast Capacity of Pre-engineered Metal Buildings using Coupled CFD and FEA Modeling

PresentationThe initial CCPS guideline [CCPS, 1996] for estimating lethality for building occupants within petrochemical buildings subjected to blast hazards was based on building construction type and peak overpressure. This method allows for a quick screening of building occupant vulnerability but does not include the effects of the duration of the blast that the buildings are subjected to. Blast hazards within petrochemical facilities include vapor cloud explosions (VCE), BLEVEs, and bursting pressure vessels. VCE’s include both deflagrations having long blast durations and detonations having much shorter durations. Bursting pressure vessels can also be characterized as having relatively short durations. Therefore, the latest CCPS guideline [CCPS, 2012] removed this singular peak overpressure methodology and provided occupant vulnerability as a function of building damage and construction type as a function of peak overpressure and duration. Unfortunately, this improved method on blast characterization did not provide a way to correlate blast loading with building damage. This blast-to-damage correlation is required to conduct quantitative risk assessments. A range of simplified tools are available for assessing the response of structural components and building construction types to blast loads. These tools include Single Degree of Freedom (SDOF) models and Pressure-Impulse (P-I) iso-damage charts. These simplified tools generally do not account for the complex response and failure of real structures or the difference in response to different forms of blast loading that include finite rise times (blast waves). Iso-damage charts may be based upon historical data gathered from a range of sources and are often based upon blast damage caused by High Explosive (HE) detonations. This presentation illustrates the use of multi-degree of freedom structural systems for a pre- engineered metal building (PEMB). PEMBs represent the majority of building construction within petrochemical facilities. Computational Structural Dynamic (CSD) finite element analysis (FEA) and Computational Fluid Dynamic (CFD) approaches are used to show the level of conservatism in estimating the blast capacity of PEMBs compared to more traditional SDOF methods. Fully coupled CFD and FEA modeling that includes the beneficial effect of including the air that is internal to the building is demonstrated

Up-down instability of binary black holes in numerical relativity

Binary black holes with spins that are aligned with the orbital angular momentum do not precess. However, post-Newtonian calculations predict that "up-down" binaries, in which the spin of the heavier (lighter) black hole is aligned (antialigned) with the orbital angular momentum, are unstable when the spins are slightly perturbed from perfect alignment. This instability provides a possible mechanism for the formation of precessing binaries in environments where sources are preferentially formed with (anti) aligned spins. In this paper, we present the first full numerical relativity simulations capturing this instability. These simulations span $\sim 100$ orbits and $\sim 3$-$5$ precession cycles before merger, making them some of the longest numerical relativity simulations to date. Initialized with a small perturbation of $1^{\circ}$-$10^{\circ}$, the instability causes a dramatic growth of the spin misalignments, which can reach $\sim 90^{\circ}$ near merger. We show that this leaves a strong imprint on the subdominant modes of the gravitational wave signal, which can potentially be used to distinguish up-down binaries from other sources. Finally, we show that post-Newtonian and effective-one-body approximants are able to reproduce the unstable dynamics of up-down binaries extracted from numerical relativity

Molecular definition of a narrow interval at 7q22.1 associated with myelodysplasia

Chromosome 7 translocations, deletions, or monosomy are associated with myelodysplasia (MDS) and acute myeloid leukemia both in children and adults. These chromosomal anomalies represent one of the most common cytogenetic abnormalities associated with these diseases and usually herald a poor prognosis. In this study two cosmid DNA probes that mapped to 7q22.1 and were known to be separated by approximately 500 kb were identified to flank the proximal inversion breakpoint in a patient carrying a constitutional inversion (7q22.1-34) associated with MDS. A yeast artificial chromosome (YAC) clone that encompassed the two cosmids was identified and shown to span the breakpoint. Fluorescence in situ hybridization was then used to analyze six additional patients with myelodysplasia and chromosomal rearrangements of the 7q22 region (three patients had translocations and three carried deletions). The breakpoint in one of the patients was found to be contained within the same YAC clone that spanned the inversion breakpoint. Moreover, this same interval was determined to be absent in all three patients with chromosomal deletions. These results suggest that this segment of DNA on chromosome 7q22.1 may contain specific gene(s) that have a significant role in myeloid malignancies.link_to_OA_fulltex

The protein import apparatus of chloroplasts

Routing of cytosolically synthesized precursor proteins into chloroplasts is a specific process which involves a multitude of soluble and membrane components. In this review we wil1 focus on early events of the translocation pathway of nuclear coded plastidic precursor proteins and compare import routes for polypeptide of the outer chloroplast envelope to that of internal chloroplast compartments. A number of proteins housed in the chloroplast envelopes have been implied to be involved in the translocation process, but so far a certain function has not been assigned to any of these proteins. The only exception could be an envelope localized hsc 70 homologue which could retain the import competence of a precursor protein in transit into the organelle

Ray Tracing Simulations of Weak Lensing by Large-Scale Structure

We investigate weak lensing by large-scale structure using ray tracing through N-body simulations. Photon trajectories are followed through high resolution simulations of structure formation to make simulated maps of shear and convergence on the sky. Tests with varying numerical parameters are used to calibrate the accuracy of computed lensing statistics on angular scales from about 1 arcminute to a few degrees. Various aspects of the weak lensing approximation are also tested. For fields a few degrees on a side the shear power spectrum is almost entirely in the nonlinear regime and agrees well with nonlinear analytical predictions. Sampling fluctuations in power spectrum estimates are investigated by comparing several ray tracing realizations of a given model. For survey areas smaller than a degree on a side the main source of scatter is nonlinear coupling to modes larger than the survey. We develop a method which uses this effect to estimate the mass density parameter Omega from the scatter in power spectrum estimates for subregions of a larger survey. We show that the power spectrum can be measured accurately from realistically noisy data on scales corresponding to 1-10 Mpc/h. Non-Gaussian features in the one point distribution function of the weak lensing convergence (reconstructed from the shear) are also sensitive to Omega. We suggest several techniques for estimating Omega in the presence of noise and compare their statistical power, robustness and simplicity. With realistic noise Omega can be determined to within 0.1-0.2 from a deep survey of several square degrees.Comment: 59 pages, 22 figures included. Matches version accepted for Ap

A Database of Cepheid Distance Moduli and TRGB, GCLF, PNLF and SBF Data Useful for Distance Determinations

We present a compilation of Cepheid distance moduli and data for four secondary distance indicators that employ stars in the old stellar populations: the planetary nebula luminosity function (PNLF), the globular cluster luminosity function (GCLF), the tip of the red giant branch (TRGB), and the surface brightness fluctuation (SBF) method. The database includes all data published as of July 15, 1999. The main strength of this compilation resides in all data being on a consistent and homogeneous system: all Cepheid distances are derived using the same calibration of the period-luminosity relation, the treatment of errors is consistent for all indicators, measurements which are not considered reliable are excluded. As such, the database is ideal for inter-comparing any of the distance indicators considered, or for deriving a Cepheid calibration to any secondary distance indicator. Specifically, the database includes: 1) Cepheid distances, extinctions and metallicities; 2) apparent magnitudes of the PNLF cutoff; 3) apparent magnitudes and colors of the turnover of the GCLF (both in the V- and B-bands); 4) apparent magnitudes of the TRGB (in the I-band) and V-I colors at and 0.5 magnitudes fainter than the TRGB; 5) apparent surface brightness fluctuation magnitudes I, K', K_short, and using the F814W filter with the HST/WFPC2. In addition, for every galaxy in the database we give reddening estimates from DIRBE/IRAS as well as HI maps, J2000 coordinates, Hubble and T-type morphological classification, apparent total magnitude in B, and systemic velocity. (Abridged)Comment: Accepted for publication in the Astrophysical Journal Supplement Series. Because of space limitations, the figures included are low resolution bitmap images. Original figures can be found at http://www.astro.ucla.edu/~laura/pub.ht

The Extragalactic Distance Scale Key Project XXVII. A Derivation of the Hubble Constant Using the Fundamental Plane and Dn-Sigma Relations in Leo I, Virgo, and Fornax

Using published photometry and spectroscopy, we construct the fundamental plane and D_n-Sigma relations in Leo I, Virgo and Fornax. The published Cepheid P-L relations to spirals in these clusters fixes the relation between angular size and metric distance for both the fundamental plane and D_n-Sigma relations. Using the locally calibrated fundamental plane, we infer distances to a sample of clusters with a mean redshift of cz \approx 6000 \kms, and derive a value of H_0=78+- 5+- 9 km/s/Mpc (random, systematic) for the local expansion rate. This value includes a correction for depth effects in the Cepheid distances to the nearby clusters, which decreased the deduced value of the expansion rate by 5% +- 5%. If one further adopts the metallicity correction to the Cepheid PL relation, as derived by the Key Project, the value of the Hubble constant would decrease by a further 6%+- 4%. These two sources of systematic error, when combined with a +- 6% error due to the uncertainty in the distance to the Large Magellanic Cloud, a +- 4% error due to uncertainties in the WFPC2 calibration, and several small sources of uncertainty in the fundamental plane analysis, combine to yield a total systematic uncertainty of +- 11%. We find that the values obtained using either the CMB, or a flow-field model, for the reference frame of the distant clusters, agree to within 1%. The Dn-Sigma relation also produces similar results, as expected from the correlated nature of the two scaling relations. A complete discussion of the sources of random and systematic error in this determination of the Hubble constant is also given, in order to facilitate comparison with the other secondary indicators being used by the Key Project.Comment: 21 pages, 3 figures, Accepted for publication in Ap

The disruption of nearby galaxies by the Milky Way

Interactions between galaxies are common and are an important factor in determining their physical properties such as position along the Hubble sequence and star-formation rate. There are many possible galaxy interaction mechanisms, including merging, ram-pressure stripping, gas compression, gravitational interaction and cluster tides. The relative importance of these mechanisms is often not clear, as their strength depends on poorly known parameters such as the density, extent and nature of the massive dark halos that surround galaxies. A nearby example of a galaxy interaction where the mechanism is controversial is that between our own Galaxy and two of its neighbours -- the Large and Small Magellanic Clouds. Here we present the first results of a new HI survey which provides a spectacular view of this interaction. In addition to the previously known Magellanic Stream, which trails 100 degrees behind the Clouds, the new data reveal a counter-stream which lies in the opposite direction and leads the motion of the Clouds. This result supports the gravitational model in which leading and trailing streams are tidally torn from the body of the Magellanic Clouds.Comment: 17 pages with 5 figures in gif format, scheduled for publication in the August 20th, 1998 issue of Natur

HIPASS Detection of an Intergalactic Gas Cloud in the NGC 2442 Group

We report the discovery, from the HI Parkes All-Sky Survey (HIPASS), of a gas cloud associated with the asymmetric spiral galaxy NGC 2442. This object, designated HIPASS J0731-69, contains ~10^9 M_sun of HI, or nearly one-third as much atomic gas as NGC 2442 itself. No optical counterpart to any part of HIPASS J0731-69 has yet been identified, consistent with the gas being diffuse, and with its stream-like kinematics. If the gas in HIPASS J0731-69 was once part of NGC 2442, then it was most likely a fairly recent tidal encounter with a moderately massive companion which tore it loose, although the possibility of ram-pressure stripping cannot be ruled out. This discovery highlights the potential of the HIPASS data for yielding new clues to the nature of some of the best-known galaxies in the local universe.Comment: 8 pages, 4 figures, uses "emulateapj5.sty". Accepted for publication in ApJ, Vol. 555, 1 July 2001. Figs 1 and 2 included as JPE